Femoral component for a knee prosthesis with improved articular characteristics

ABSTRACT

An orthopaedic knee prosthesis includes a femoral component which exhibits enhanced articular features, minimizes removal of healthy bone stock from the distal femur, and minimizes the impact of the prosthesis on adjacent soft tissues of the knee.

BACKGROUND 1. Technical Field

The present disclosure relates to orthopaedic prostheses and,specifically, to femoral components in a knee prosthesis.

2. Description of the Related Art

Orthopaedic prostheses are commonly utilized to repair and/or replacedamaged bone and tissue in the human body. For a damaged knee, a kneeprosthesis may be implanted using a tibial base plate, a tibial bearingcomponent, and a distal femoral component. The tibial base plate isaffixed to a proximal end of the patient's tibia, which is typicallyresected to accept the base plate. The femoral component is implanted ona distal end of the patient's femur, which is also typically resected toaccept the femoral component. The tibial bearing component is placedbetween the tibial base plate and femoral component, and may be fixedlyor slidably coupled to the tibial base plate.

The femoral component provides articular surfaces which interact withthe adjacent tibial bearing component and a natural or prostheticpatella during extension and flexion of the knee. The features andgeometry of the articular surfaces of the femoral component influencethe articular characteristics of the knee, such as by cooperating withthe tibial bearing component to define flexion range, internal/externalrotation, femoral rollback and patellar tracking, for example. Thenonarticular, bone contacting surfaces of the femoral component definethe shape and geometry of the bone resection on the distal femur, andtherefore influence the amount of bone resected from the femur.

Further, the overall shape and geometry of the femoral component,particularly around its outer periphery, influences the interactionbetween the knee prosthesis and adjacent soft tissues remaining in placeafter prosthesis implantation.

Accordingly, substantial design efforts have focused on providing kneeprosthesis components which preserve flexion range, promote desirablekinematic motion profiles, protect natural soft tissues, and arecompatible with the widest possible range of prospective kneereplacement patients.

SUMMARY

The present disclosure provides an orthopaedic knee prosthesis includinga femoral component which exhibits enhanced articular features,minimizes removal of healthy bone stock from the distal femur, andminimizes the impact of the prosthesis on adjacent soft tissues of theknee.

Features which operate to enhance articulation include: 1) bulbousposterior geometry of the femoral condyles, as viewed in a sagittalcross-section (i.e., the “J-curve”), facilitates deep flexion and lowcomponent wear by reconfiguring the J-curve curvature at flexion levelsabove 90-degrees; 2) provision of “standard” and “narrow” femoralcomponents which share a common bone-resection sagittal profile butdefine different peripheral and articular geometries designed toaccommodate natural variability in patient anatomy; and 3) a lateralposterior femoral condyle which is shorter (i.e., defines a reducedproximal/distal dimension) as compared to the medial posterior condyle,thereby facilitating deep flexion and the attendant external rotation ofthe femur while avoiding impingement between prosthesis components.

Features which operate to minimize impact of the prosthesis on adjacentsoft tissues of the knee include: 1) for posterior-stabilized (PS)designs, a femoral cam with a generally cylindrical articular surface,in which the articular surface is flanked at its medial and lateral endsby broad, large-radius convex-to-concave transitions to the adjacentmedial and lateral femoral condyles, thereby ensuring a desiredcam/spine articular interaction while avoiding potential soft-tissueimpingement; 2) for cruciate retaining (CR) designs, an asymmetricintercondylar notch which accommodates external rotation of the femur indeep flexion while avoiding impingement between intercondylar wallsurfaces and the posterior cruciate ligament; and 3) an anterior flangeincluding a patellofemoral groove or sulcus, in which the medial andlateral surfaces near the edge of the flange define broad, large-radiusconvexity, thereby accommodating soft tissues in the anterior portion ofthe knee.

Features which allow femoral components made in accordance with thepresent disclosure to be implanted with minimal bone removal include: 1)an anterior bone contacting surface, opposite the patellar groove of theanterior flange, which includes an edged central peak operable tomaintain a desired material thickness throughout the anterior flangewhile reducing the overall average thickness of the anterior flange; 2)for posterior-stabilized (PS) implant designs, an intercondylar box withsloped sidewalls which selectively reduce the proximal/distal height ofportions of the sidewalls, to facilitate preservation of bone near theanterior end of the anatomic intercondylar notch; 3) for PS designs,intercondylar box sidewalls which are configured to function as afixation lug, thereby obviating the need for fixation pegs; 4)consistently small incremental growth between respective pairs ofprosthesis sizes, thereby allowing minimal bone resection for a greatermajority of patients; and 5) a specially designed “pocket” on the bonecontacting side of the femoral component for bone cement and/or porousbone-ingrowth material, in which the pocket maximizes long-term fixationwhile also facilitating potential component removal in revision surgery.

According to one embodiment thereof, the present invention provides aposterior-stabilized femoral component adapted to articulate with atibial bearing component in a knee prosthesis, the tibial bearingcomponent including a proximally extending spine, the femoral componentcomprising: medial and lateral condyles shaped to articulate with thetibial bearing component through a range of motion, in which fullextension corresponds to zero degrees flexion of the knee prosthesis andpositive flexion corresponds to greater than zero degrees flexion of theknee prosthesis, the medial and lateral condyles comprising inwardlyfacing condylar walls forming an intercondylar space therebetween, theintercondylar space having a medial/lateral width; and a femoral camspanning the intercondylar space to join the medial and lateral condylesto one another, the femoral cam sized and positioned to engage the spineof the tibial bearing component in positive flexion through at least aportion of the range of motion, the femoral cam having an articularsurface comprising: a central articular surface that is one ofcylindrical and convex across a medial/lateral extent of the centralarticular surface; a convex medial transition surface flanking thecentral articular surface and disposed between the central articularsurface and the medial condyle; and a convex lateral transition surfaceflanking the central articular surface and disposed between the centralarticular surface and the lateral condyle, the central articularsurface, the convex medial transition surface and the convex lateraltransition surface cooperating to occupy at least 80% of themedial/lateral width of the intercondylar space.

According to another embodiment thereof, the present invention providesa posterior-stabilized femoral component adapted to articulate with atibial bearing component in a knee prosthesis, the tibial bearingcomponent including a proximally extending spine, the femoral componentcomprising: medial and lateral condyles shaped to articulate with thetibial bearing component through a range of motion, in which fullextension corresponds to zero degrees flexion of the knee prosthesis andpositive flexion corresponds to greater than zero degrees flexion of theknee prosthesis, the medial and lateral condyles comprising inwardlyfacing condylar walls forming an intercondylar space therebetween, theintercondylar space having a medial/lateral width; and a femoral camsized and positioned to engage the spine of the tibial bearing componentin positive flexion through a portion of the range of motion, thefemoral cam comprising a medial/lateral cam length spanning theintercondylar space such that the femoral cam joins the medial andlateral condyles to one another, the femoral cam having an articularsurface comprising: a central articular surface that is one ofcylindrical and convex across a medial/lateral extent of the centralarticular surface; a convex medial transition surface flanking thecentral articular surface and disposed between the central articularsurface and the medial condyle; and a convex lateral transition surfaceflanking the central articular surface and disposed between the centralarticular surface and the lateral condyle, the convex medial transitionsurface and the convex lateral transition surface each defining an arcextending in a medial/lateral direction, the arc defining a radius equalto between 40% and 60% of the medial/lateral cam length, whereby thefemoral cam defines widely rounded, convex surfaces.

According to yet another embodiment thereof, the present inventionprovides a posterior-stabilized femoral component adapted to articulatewith a tibial bearing component in a knee prosthesis, the tibial bearingcomponent including a proximally extending spine, the femoral componentcomprising: a medial condyle comprising: a medial condylar surfaceshaped to articulate with a medial articular compartment of the tibialbearing component through a range of motion; and a medial posteriorbone-contacting surface disposed opposite the medial condylar surfaceand positioned to abut a posterior facet of a resected femur uponimplantation of the femoral component, the medial posteriorbone-contacting surface extending between a medial edge of the femoralcomponent and a medial intercondylar wall; a lateral condyle separatedfrom the medial condyle by a component sagittal plane, the lateralcondyle comprising: a lateral condylar surface shaped to articulate witha lateral articular compartment of the tibial bearing component throughthe range of motion; and a lateral posterior bone-contacting surfacedisposed opposite the lateral condylar surface and positioned to abutthe posterior facet of the resected femur upon implantation of thefemoral component, the lateral posterior bone-contacting surfaceextending between a lateral edge of the femoral component and a lateralintercondylar wall facing the medial intercondylar wall; and a patellarflange extending anteriorly from the medial and lateral condyles andshaped to articulate with a patellar articular surface, the patellarflange comprising: a flange articular surface shaped to articulate withthe patellar articular surface; an anterior bone-contacting surfacedisposed opposite the flange articular surface and positioned to abut ananterior facet of the resected femur upon implantation of the femoralcomponent; and a distal bone-contacting surface extending along ananterior/posterior space between the anterior bone-contacting surfaceand the medial and lateral posterior bone-contacting surfaces, thelateral and medial intercondylar walls each defining posterior wallportions extending proximally from the distal bone-contacting surface todefine a proximal/distal extent of the posterior wall portions, thelateral and medial intercondylar walls comprising angled lateral andmedial anterior wall portions, respectively, the angled lateral andmedial wall portions each sloping distally toward the distalbone-contacting surface to define an acute angle therewith, such thatthe lateral and medial anterior wall portions define gradually reducingproximal/distal extents as compared to the proximal/distal extent of theposterior wall portions.

According to still another embodiment thereof, the present inventionprovides a femoral component adapted to articulate with a tibialarticular surface and a patellar articular surface in a knee prosthesis,the femoral component comprising: a medial condyle comprising: a medialcondylar surface shaped to articulate with a medial compartment of thetibial articular surface through a range of motion; and a medialposterior bone-contacting surface disposed opposite the medial condylarsurface and positioned to abut a posterior facet of a resected femurupon implantation of the femoral component, the medial posteriorbone-contacting surface extending between a medial edge of the femoralcomponent and a medial intercondylar wall; a lateral condyle separatedfrom the medial condyle by a component sagittal plane, the lateralcondyle comprising: a lateral condylar surface shaped to articulate witha lateral compartment of the tibial articular surface through the rangeof motion; and a lateral posterior bone-contacting surface disposedopposite the lateral condylar surface and positioned to abut theposterior facet of the resected femur upon implantation of the femoralcomponent, the lateral posterior bone-contacting surface extendingbetween a lateral edge of the femoral component and a lateralintercondylar wall facing the medial intercondylar wall; and a patellarflange extending anteriorly from the medial and lateral condyles, thepatellar flange comprising: a flange articular surface shaped toarticulate with the patellar articular surface; an anteriorbone-contacting surface disposed opposite the flange articular surfaceand positioned to abut an anterior facet of the resected femur uponimplantation of the femoral component, the anterior bone-contactingsurface extending between the lateral edge of the femoral component andthe medial edge of the femoral component; and a distal bone-contactingsurface extending along an anterior/posterior space between the anteriorbone-contacting surface and the medial and lateral posteriorbone-contacting surfaces, the distal bone-contacting surface extendingbetween the lateral edge of the femoral component and the medial edge ofthe femoral component, the medial and lateral edges of the femoralcomponent defining an inner sagittal profile, as viewed in the componentsagittal plane such that the medial edge of the femoral component issuperimposed over the lateral edge of the femoral component, and themedial and lateral edges comprising medial and lateral rails protrudinginwardly to define a recessed pocket between the medial and lateralrails, the femoral component comprising at least one lateral fixationpeg and at least one medial fixation peg, the lateral fixation pegextending proximally from the distal bone-contacting surface and spacedlaterally away from the lateral intercondylar wall such that a lateralportion of the distal bone-contacting surface is disposed between thelateral fixation peg and the lateral intercondylar wall, the medialfixation peg extending proximally from the distal bone-contactingsurface and spaced medially away from the medial intercondylar wall suchthat a medial portion of the distal bone-contacting surface is disposedbetween the medial fixation peg and the medial intercondylar wall, atleast one of the medial portion and the lateral portion of the distalbone-contacting surface occupied by a ridge rising above the recessedpocket, the ridge elevated above the recessed pocket by substantiallythe same amount as the medial and lateral rails such that the ridge issubstantially coincident with the inner sagittal profile as viewed inthe component sagittal plane, whereby the ridge interrupts any fixationmaterial which may be contained within the recessed pocket uponimplantation of the femoral component to a distal femur.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and advantages of thisdisclosure, and the manner of attaining them, will become more apparentand the invention itself will be better understood by reference to thefollowing description of embodiments of the invention taken inconjunction with the accompanying drawings, wherein:

FIG. 1A is a bottom perspective view of a femoral component inaccordance with the present disclosure;

FIG. 1B is a side, elevation cross-section view of the femoral componentshown in FIG. 1A, taken along line 1B-1B;

FIG. 1C is an enlarged view of a portion of the femoral component shownin FIG. 1B, illustrating posterior condylar geometry as compared with analternative design;

FIG. 1D is a graph plotting the arc length per degree of angular sweepfor portions of lateral femoral J-curves corresponding to greater than90-degrees of flexion, with the illustrated data pertaining tocruciate-retaining prior art femoral components (where prior art devicesare listed as “predicate”) and cruciate-retaining femoral componentsmade in accordance with the present disclosure;

FIG. 1E is a graph plotting the arc length per degree of angular sweepfor portions of medial femoral J-curves corresponding to greater than90-degrees of flexion, with the illustrated data pertaining tocruciate-retaining prior art femoral components (where prior art devicesare listed as “predicate”) and cruciate-retaining femoral componentsmade in accordance with the present disclosure;

FIG. 1F is a graph plotting the arc length per degree of angular sweepfor portions of femoral J-curves corresponding to greater than90-degrees of flexion, with the illustrated data pertaining toposterior-stabilized prior art femoral components (where prior artdevices are listed as “predicate”) and cruciate-retaining femoralcomponents made in accordance with the present disclosure;

FIG. 2A is a side elevation, cross-sectional view of the femoralcomponent shown in FIG. 1B, in which the femoral component isarticulating with a tibial bearing component made in accordance with thepresent disclosure;

FIG. 2B is an enlarged view of a portion of the femoral component andtibial bearing component shown in FIG. 2A, illustrating a deep-flexioncontact point therebetween;

FIG. 3A is an anterior, elevation view illustrating a pair of femoralcomponents made in accordance with the present disclosure;

FIG. 3B is a sagittal, elevation view illustrating the pair of femoralcomponents of FIG. 3A;

FIG. 3C is a graph plotting the overall medial/lateral width of familiesof regular and narrow femoral components made in accordance with thepresent disclosure;

FIG. 3D is a graph plotting the proximal/distal height of the anteriorflanges of the families of femoral components shown in FIG. 3C;

FIG. 3E is a graph plotting the proximal/distal height of the lateralcondyles of the families of femoral components shown in FIG. 3C;

FIG. 3F is a graph plotting the proximal/distal height of the medialcondyles of the families of femoral components shown in FIG. 3C;

FIG. 4 is a posterior elevation, cross-sectional view of the femoralcomponent shown in FIG. 1B, illustrating the coronal articular profileof the femoral condyles;

FIG. 5A is a posterior, perspective view of a femoral component made inaccordance with the present disclosure;

FIG. 5B is a side elevation, cross-sectional view of a portion of thefemoral component shown in FIG. 5A;

FIG. 5C is a posterior elevation, cross-sectional view of the femoralcomponent shown in FIG. 5A;

FIG. 6 is a proximal, perspective view of a tibial bearing componentmade in accordance with the present disclosure;

FIG. 7 is a proximal plan view of a femoral component made in accordancewith the present disclosure;

FIG. 8 is a proximal plan, cross-sectional view of the anterior flangeof the femoral component shown in FIG. 1B, taken along line 8-8 shown inFIG. 1B;

FIG. 9A is a perspective view of the femoral component shown in FIG. 1B;

FIG. 9B is a partial, enlarged view of a portion of the femoralcomponent shown in FIG. 9A;

FIG. 10A is a sagittal elevation, cross-sectional view of a portion ofthe femoral component shown in FIG. 9A, taken along line 10A-10A of FIG.9B;

FIG. 10B is a sagittal elevation, cross-sectional view of the femoralcomponent shown in FIG. 9A, illustrating the femoral component implantedon a femur;

FIG. 10C is an anterior elevation view of the femur shown in FIG. 10B,prior to implantation of the femoral component;

FIG. 10D is an anterior elevation view of the femur shown in FIG. 10B,after implantation of the femoral component;

FIG. 11A is a sagittal elevation, cross-sectional view of a femoralcomponent made in accordance with the present disclosure, shown with afemur resected to receive the femoral component;

FIG. 11B is a sagittal elevation, cross-sectional view of the femoralcomponent of FIG. 11A, illustrating interaction between an intercondylarbox thereof and the femur after implantation;

FIG. 12A is a proximal perspective view of a femoral component made inaccordance with the present disclosure;

FIG. 12B is an enlarged view of a portion of the femoral component shownin FIG. 12A, illustrating an intercondylar box sidewall thereof;

FIG. 12C is an enlarged view of a portion of the femoral component shownin FIG. 12A, illustrating an intercondylar box sidewall thereof;

FIG. 12D is a proximal perspective view of another femoral componentmade in accordance with the present disclosure;

FIG. 13A is a sagittal, elevation view illustrating a pair ofdifferently sized femoral components made in accordance with the presentdisclosure;

FIG. 13B is a graph plotting the functional anterior/posterior extentsof the differently sized femoral components of FIG. 13A, as compared toprior art devices;

FIG. 14A is a proximal perspective view of the femoral component of FIG.1B, illustrating osteotome access thereto; and

FIG. 14B is a proximal perspective view of the femoral component shownin FIG. 5A, illustrating osteotome access thereto.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate exemplary embodiments of the present invention, and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

The present disclosure provides a femoral component for a kneeprosthesis which contributes to preservation of healthy bone stock,enhanced articular characteristics, and reduced impact on soft tissuesof the knee.

In order to prepare the tibia and femur for receipt of a knee jointprosthesis of the present disclosure, any suitable methods orapparatuses for preparation of the knee joint may be used. Exemplarysurgical procedures and associated surgical instruments are disclosed in“Zimmer LPS-Flex Fixed Bearing Knee, Surgical Technique”, “NEXGENCOMPLETE KNEE SOLUTION, Surgical Technique for the CR-Flex Fixed BearingKnee” and “Zimmer NexGen Complete Knee SolutionExtramedullary/Intramedullary Tibial Resector, Surgical Technique”(collectively, the “Zimmer Surgical Techniques”), the entire disclosuresof which are hereby expressly incorporated herein by reference, copiesof which are filed in an information disclosure statement on even dateherewith. A surgeon first provides a prosthetic component by procuringan appropriate component (e.g., such as femoral component 20) for use inthe surgical procedure, such as from a kit or operating-room containeror storage receptacle. The surgeon then implants the component usingsuitable methods and apparatuses, such as the methods and apparatusesdescribed in the Zimmer Surgical Techniques.

As used herein, “proximal” refers to a direction generally toward thetorso of a patient, and “distal” refers to the opposite direction ofproximal, i.e., away from the torso of a patient. “Anterior” refers to adirection generally toward the front of a patient or knee, and“posterior” refers to the opposite direction of anterior, i.e., towardthe back of the patient or knee. In the context of a prosthesis alone,such directions correspond to the orientation of the prosthesis afterimplantation, such that a proximal portion of the prosthesis is thatportion which will ordinarily be closest to the torso of the patient,the anterior portion closest to the front of the patient's knee, etc.

Similarly, knee prostheses in accordance with the present disclosure maybe referred to in the context of a coordinate system includingtransverse, coronal and sagittal planes of the component. Uponimplantation of the prosthesis and with a patient in a standingposition, a transverse plane of the knee prosthesis is generallyparallel to an anatomic transverse plane, i.e., the transverse plane ofthe knee prosthesis is inclusive of imaginary vectors extending alongmedial/lateral and anterior/posterior directions. However, it iscontemplated that in some instances the bearing component transverseplane will be slightly angled with respect to the anatomic transverseplane, depending, e.g., on the particular surgical implantationtechnique employed by the surgeon.

Coronal and sagittal planes of the knee prosthesis are also generallyparallel to the coronal and sagittal anatomic planes in a similarfashion. Thus, a coronal plane of the prosthesis is inclusive of vectorsextending along proximal/distal and medial/lateral directions, and asagittal plane is inclusive of vectors extending alonganterior/posterior and proximal/distal directions. As with therelationship between the anatomic and bearing component transverseplanes discussed above, it is appreciated that small angles may beformed between the bearing component sagittal and coronal planes and thecorresponding anatomic sagittal and coronal planes depending upon thesurgical implantation method.

As with anatomic planes, the sagittal, coronal and transverse planesdefined by the knee prosthesis are mutually perpendicular to oneanother. For purposes of the present disclosure, reference to sagittal,coronal and transverse planes is with respect to the present kneeprosthesis unless otherwise specified.

In the context of the femoral component in some knee prostheses, asagittal plane may be a plane this is equidistant from intercondylarwalls bounding the intercondylar gap formed by the component condyles.For example, referring to FIG. 5A, femoral component 220 definesintercondylar notch or gap 268 formed between lateral and medialintercondylar walls 238, 239 (FIG. 5C). In this context of component220, a sagittal plane may the plane which bisects intercondylar gap 268and is equidistant from intercondylar walls 238, 239.

Where the sagittal plane discussed above forms the basis for thecomponent coordinate system, a coronal plane would be defined as a planeperpendicular to the sagittal plane and extending along the sameproximal/distal direction as the sagittal plane. A transverse plane isthe plane perpendicular to both the sagittal and coronal planes.

In other instances, it may be appropriate to define transverse plane asthe plane perpendicular to one or both of distal most points 30, 32(FIG. 1B) defined by lateral and medial condyles 24, 26. Generallyspeaking, the “distal-most points” of a femoral component of a kneeprosthesis are those points which make the distal-most contact with thecorresponding tibial bearing component or natural tibial articularsurface when the knee is fully extended. Similarly, the “posterior-mostpoints” of a femoral component of a knee prosthesis are those pointswhich make contact with the corresponding tibial bearing component whenthe knee is at 90-degrees flexion, i.e., when the anatomic femoral andtibial axes form an angle of 90 degrees.

In the illustrative embodiment of FIG. 1A, lateral and medial condyles24, 26 each define bearing surfaces that are three-dimensionally convexat distal-most points 30, 32. Stated another way, the lateral and medialarticular bearing surfaces have no planar portions at distal-most points30, 32. Recognizing that a three-dimensionally convex surface can defineonly one tangent plane at a particular point, the transverse plane offemoral component 20 may be defined as the plane tangent to one or bothof distal-most points 30, 32. For many femoral components, transverseplanes tangent to each of distal-most points 30, 32, are coplanar ornearly coplanar, such that a selection of either of distal-most points30, 32 is suitable as a reference point for definition of the componenttransverse plane.

Where the above-described transverse plane is the basis for thecomponent coordinate system, a coronal plane may be defined as beingperpendicular to the transverse plane and extending along the samemedial/lateral direction as the transverse plane. Alternatively, thecoronal plane may be defined as a plane tangent to one or both ofposterior-most points 34, 36 in similar fashion to the tangency of thetransverse plane to distal-most points 30, 32 as discussed above. Ineither instance, the sagittal plane can then be defined as a planeperpendicular to the coronal and transverse planes.

Practically speaking, femoral prostheses are sold with a particularsurgical procedure envisioned for component implantation. Depending onthe particular geometry and accompanying surgical procedure, a personhaving ordinary skill in the art of orthopaedic prostheses will be ableto define “distal-most points” of a femoral prosthesis component, andwill be able to identify the sagittal, coronal and transverse componentcoordinate planes based on their relationship to the correspondinganatomic planes upon implantation.

The embodiments shown and described herein illustrate components for aleft knee prosthesis. Right and left knee prosthesis configurations aremirror images of one another about a sagittal plane. Thus, it will beappreciated that the aspects of the prosthesis described herein areequally applicable to a left or right knee configuration.

Prosthesis designs in accordance with the present disclosure may includeposterior stabilized (PS) prostheses and mid level constraint (MLC)prostheses, each of which includes spine 278 (FIG. 6) on the tibialbearing component and femoral cam 276 (FIG. 5A) on the femoralcomponent. Spine 278 and cam 276 are designed to cooperate with oneanother to stabilize femoral component 220 with respect to tibialbearing component 240 in lieu of a resected posterior cruciate ligament(PCL).

Another contemplated design includes “cruciate retaining” (CR)prostheses, such as those using components configured as shown in FIGS.1A, 2A (shown by solid lines) and 4. CR designs omit spine 278 from thetibial bearing component and femoral cam 276 from the femoral component(e.g., FIG. 9A), such that cruciate-retaining femoral component 20defines an intercondylar space between lateral and medial condyles 24,26 that is entirely open and uninterrupted by femoral cam 276. CR tibialcomponents are generally used in surgical procedures which retain thePCL.

Yet another design includes “ultra congruent” (UC) prostheses, which mayuse a femoral component lacking femoral cam 276, and may be similar oridentical to the femoral component used in a CR prosthesis (i.e.,femoral component 20 shown in FIG. 9A). Like CR prostheses, UCprostheses also omit spine 278 (e.g., the solid-line embodiment of FIG.2A). However, UC prostheses are designed for use with a patient whosePCL is resected during the knee replacement surgery. “Congruence,” inthe context of knee prostheses, refers to the similarity of curvaturebetween the convex femoral condyles and the correspondingly concavetibial articular compartments. UC designs utilize very high congruencebetween the tibial bearing compartments and femoral condyles to provideprosthesis stability, particularly with respect to anterior/posteriorrelative motion.

Except as otherwise specified herein, all features described below maybe used with any potential prosthesis design. While a particular designmay include all the features described herein, it is contemplated thatsome prostheses may omit some features described herein, as required ordesired for a particular application.

1. Articular Features: Bulbous Sagittal Posterior Geometry.

Referring to FIG. 1B, femoral component 20 includes anterior flange 22,lateral condyle 24 and opposing medial condyle 26, and fixation pegs 28.Lateral and medial condyles 24, 26 define articular surfaces whichextend from respective lateral and medial distal-most contact points 30,32 (FIG. 4), through respective lateral and medial posterior-mostcontact points 34, 36 (FIG. 7) and terminate at respective deep flexioncontact areas as described in detail below. The articular surfaces arerounded and convex in shape, and sized and shaped to articulate with atibial articular surface through a full range of motion from fullextension of the knee (i.e., zero degrees flexion) through mid-flexionand deep-flexion. In an exemplary embodiment, such tibial articularsurfaces are correspondingly concave dished surfaces of a prosthetictibial component (e.g., tibial bearing component 240 of FIG. 6).However, it is appreciated that in some instances the tibial articularsurface may be the natural articular compartments of a patient's tibia.

Distal-most contact points 30, 32 contact a tibial bearing component ofthe knee prosthesis (such as tibial bearing component 40 shown in FIG.2A) when the knee prosthesis is at zero degrees of flexion, i.e., whenthe knee is fully extended, as noted above. As the knee is flexed fromfull extension, the lateral and medial contact points between femoralcomponent 20 and the adjacent tibial articular surface shift posteriorlyand proximally into an initial-flexion segment along medial and lateralJ-curves 27M, 27L (FIG. 1A), passing through intermediate levels offlexion to eventually reach posterior most contact points 34, 36 at 90degrees flexion. Further flexion transitions such contact points furtherproximally, and also anteriorly (i.e., toward anterior flange 22) into adeep-flexion segment of J-curves 27M, 27L.

For convenience, the present discussion refers to “points” or “lines” ofcontact between tibial bearing component 40 and femoral component 20.However, it is of course appreciated that each potential point or lineof contact is not truly a point or line, but rather an area of contact.These areas of contact may be relatively larger or smaller depending onvarious factors, such as prosthesis materials, the amount of pressureapplied at the interface between tibial bearing component 40 and femoralcomponent 20, and the like. In an exemplary embodiment, for example,tibial bearing component 40 is made of a polymeric material such aspolyethylene, while femoral component 20 is made of a metallic materialsuch as cobalt-chrome-molybdenum (CoCrMo).

Moreover, it is appreciated that some of the factors affecting the sizeof the contact area may change dynamically during prosthesis use, suchas the amount of applied pressure at the femoral/tibial interface duringwalking, climbing stairs or crouching, for example. For purposes of thepresent discussion, a “contact point” may be taken as the point at thegeometric center of the area of contact. The “geometric center”, inturn, refers to the intersection of all straight lines that divide agiven area into two parts of equal moment about each respective line.Stated another way, a geometric center may be said to be the “average”(i.e., arithmetic mean) of all points of the given area. Similarly, a“contact line” is the central line of contact passing through andbisecting an elongate area of contact.

Taken from the sagittal perspective (FIG. 1B), anterior flange 22 andcondyles 24, 26 cooperate to define an overall U-shaped profile offemoral component 20. The articular surface of femoral component 20,along the outer surface of this U-shaped profile, defines medial andlateral J-curves 27M, 27L respectively (FIG. 1A). More specifically, thearticular surface of lateral condyle 24 cooperates with the articularsurface of anterior flange 22 to define lateral J-curve 27L, which isinclusive of distal-most contact point 30 and posterior-most contactpoint 34. Similarly, medial J-curve 27M is defined by the articularsurfaces of anterior flange 22 and medial condyle 26, taken in asagittal cross-section and inclusive of distal-most contact point 32 andposterior-most contact point 36.

Where J-curves 27L, 27M define the sagittal articular profile of femoralcomponent 20, coronal curves 64L, 64M define the corresponding coronalarticular profile. Lateral coronal curve 64L extends along a generallymedial/lateral direction, passing through lateral distal-most contactpoint 30 perpendicular to J-curve 27L. Similarly, medial coronal curve64M extends along a generally medial/lateral direction, passing throughmedial distal-most contact point 32 perpendicular to J-curve 27M. Thearticular surfaces of lateral and medial condyles 24, 26 may be definedor “built” by sweeping coronal curves 64L, 64M along J-curves 27L, 27Mrespectively to produce convex three-dimensional articular surfacesgenerally corresponding with the shape of the natural femoral condyles.The specific curvatures of coronal curves 64L, 64M may vary over theextent of J-curves 27L, 27M, such as by having a generally larger radiusat distal-most points 30, 32 as compared to posterior-most points 34,36. It is contemplated that coronal curves 64L, 64M may have a varietyof particular geometrical arrangements as required or desired for aparticular application.

The portions of J-curves 27L, 27M which articulate with lateral andmedial articular compartments 46, 48 (FIG. 6) of tibial bearingcomponent 40 extend from approximately distal-most points 30, 32,through posterior-most contact points 34, 36 and into the portion ofJ-curves 27L, 27M including bulbous profile 42, shown in FIG. 1C. Statedanother way, the condylar articular portions of J-curves 27L, 27M are acollection of the contact points between femoral condyles 24, 26 andtibial articular compartments 46, 48 respectively. The J-curve geometryillustrated in FIG. 1C is common to both lateral condyle 24 and medialcondyle 26. For clarity, however, such geometry is described herein onlywith respect to lateral condyle 24.

Condyle 24A of a predicate design is shown schematically in FIG. 1C asdashed lines, while condyle 24 of femoral component 20 is shown in solidlines. As compared with condyle 24A, condyle 24 defines bulbous profile42 in the portion of lateral J-curve 27L of condyle 24 corresponding togreater than 90 degrees of prosthesis flexion. Medial J-curve 27M ofmedial condyle 26 (shown behind lateral condyle 24 in FIG. 1B andextending further proximally, as described in detail below) also definesa similar bulbous geometry in the portion of J-curve 27M correspondingto greater than 90 degrees flexion. For simplicity, the bulbous condylargeometry of condyles 24, 26 is described with reference to lateralcondyle 24 only.

As illustrated, bulbous profile 42 extends further posteriorly andproximally than the corresponding predicate profile 42A. This bulbousgeometry arises from a reduction in the average magnitude of radius Rdefined throughout angular sweep α of profile 42, such that radius R isless than the corresponding average magnitude of radius R_(A) of profile42A through angular sweep α_(A). It is contemplated that one or moreradii may be defined through angular sweeps α, α_(A). Comparisons of theaverage radii, rather than individual radius values, are appropriatewhere multiple different radii cooperate to form profile 42 of J-curve27L and/or the corresponding predicate profile 42A. For example, incertain exemplary embodiments femoral component 20 may define an averageradius R of 10 mm while the average magnitude of radius R_(A) may be10.8 mm over a similar angular sweep. As described in detail below, theresulting bulbous overall arrangement of profile 42 advantageouslyinfluences the articular characteristics of femoral component 20 in deepflexion while minimizing bone resection.

Prior art devices relevant to deep-flexion bulbous sagittal geometryinclude the femoral components of the NexGen CR Flex prosthesis systemand the femoral components NexGen LPS Flex prosthesis system, allavailable from Zimmer, Inc. of Warsaw, Ind. The prior art Zimmer NexGenCR Flex prosthesis system is depicted in “NEXGEN COMPLETE KNEE SOLUTION,Surgical Technique for the CR-Flex Fixed Bearing Knee,” incorporated byreference above. The prior art Zimmer NexGen LPS Flex prosthesis systemis depicted in “Zimmer LPS-Flex Fixed Bearing Knee, Surgical Technique,”also incorporated by reference above.

As noted above, radii R are swept through angular extents α, α_(A).Angular extents α, α_(A) begins in the area of posterior most point 34,such as within 10 degrees of posterior-most point 34, and ends at ornear the proximal-most point of the articular surface of lateral condyle24. Referring to FIG. 1C, this proximal-most point of the articularsurface is at the intersection between the end of J-curve 27L andposterior bone-contacting surface 58. It is contemplated that terminalprofile 44 may be disposed between the proximal end of bulbous profile42 and posterior bone contacting surface 58 (As shown in FIG. 1C). Ifincluded, terminal profile 44 is a nearly flat or very large-radiusnonarticular portion of condyle 24 which bridges the gap between bulbousprofile 42 and posterior bone contacting surface 58. In an exemplaryembodiment, however, bulbous profiles 42 extend all the way to posteriorbone-contacting surface 58. Further, this exemplary femoral component 20has a substantially planar bone-contacting surface 58 which forms obtuseangle 57 with distal bone-contacting surface 54. Anteriorbone-contacting surface 50 also diverges proximally from posteriorbone-contacting surface 58 in the sagittal perspective, such thatfemoral component 20 is implantable onto a resected distal femur along adistal-to-proximal direction.

In the illustrated embodiment, the proximal terminus of angular extent a(i.e., the deepest-flexion portion of bulbous profile 42) correspondswith up to 170 degrees of knee flexion. Because femoral component 20facilitates this high level flexion of the knee, component 20 may bereferred to as a “high flexion” type component, though it is appreciatedthat any component which enables flexion of at least 130 degrees wouldalso be considered “high flexion.” In exemplary embodiments, ahigh-flexion knee prosthesis may enable a flexion range of as little as130 degrees, 135 degrees, or 140 degrees and as large as 150 degrees,155 degrees or 170 degrees, or may enable any level of flexion withinany range defined by any of the foregoing values.

For example, as illustrated in FIGS. 2A and 2B, femoral component 20 isillustrated in a deep flexion orientation, i.e., an orientation in whichflexion angle θ between longitudinal tibial axis A_(T) and longitudinalfemoral axis A_(F) is between 130 degrees and 170 degrees. As best shownin FIG. 2B, bulbous profile 42 remains in firm contact with lateralarticular compartment 46 of tibial bearing component 40 at this deepflexion configuration, thereby establishing femoral component 20 as acomponent which is deep flexion enabling. As described in detail below,femoral component 20 accomplishes this high-flexion facilitation with areduced condyle thickness as compared to prior art high-flexion typecomponents.

Determination of whether the sagittal profiles 42, 42A are relativelymore or less “bulbous” within the meaning of the present disclosure canbe accomplished by a comparison of radii R, R_(A) as described above.However, because angular sweeps α, as may differ, a suitable comparativequantity may be the amount of arc length per degree of angular sweepreferred to herein as the “bulbousness ratio.” A more bulbous geometry,(i.e., one having a smaller average radius) defines a shorter arc lengthper degree of sweep as compared to a comparable less-bulbous geometry.That is to say, a lower bulbousness ratio value corresponds to a morebulbous sagittal geometry across a given angular sweep. Given the directcorrespondence between bulbousness and radius, a relatively smalleraverage radius (i.e., radius R as compared to radius R_(A), as shown inFIG. 1C) yields a correspondingly larger bulbousness ratio across acomparable angular sweep.

Turning now to FIG. 1D, a comparison of bulbousness ratios defined byprofiles 42, 42A are shown across various prosthesis sizes for lateralcondyles 24 and 24A. For purposes of the bulbousness comparisonsdiscussed herein, angular sweeps α, α_(A) (FIG. 1C) are taken fromposterior-most points 34, 36, (i.e., at 90-degrees flexion) through theend of the corresponding J-curve (i.e., at the intersection betweenJ-curves 27L, 27M, 27A and posterior bone-contacting surface 58, 58Arespectively).

As illustrated in FIG. 1D, a dotted-line data set illustrates that thelateral condyles of the femoral components of the prior art ZimmerNexGen CR Flex prosthesis system define a bulbousness ratio of between0.190 mm/degree (for the smallest nominal size) and 0.254 mm/degree (forthe largest nominal size), while the dashed-line data set illustrates analternative subset of lateral condyles within the prior art ZimmerNexGen CR Flex prosthesis system defining a bulbousness ratio of between0.231 mm/degree and 0.246 mm/degree across a range of sizes. Femoralcomponents made in accordance with the present disclosure define abulbousness ratio of between 0.177 mm/degree (for the smallest nominalsize) and 0.219 mm/degree (for the largest nominal size), with eachcomparable size of the present components having a bulbousness ratiobelow the comparable size of the prior art devices (as shown).

For purposes of the present disclosure, anteroposterior sizing extent340 (FIG. 13A) can be considered a proxy for nominal sizes of thepresent femoral component and prior art devices. Anteroposterior sizingextent 340 may also be referred to the “functional” anterior/posteriorextent of femoral component 20, because extent 340 traverses the portionof femoral component 20 which is most relevant to tibiofemoralarticulation (and excludes the articular portions of anterior flange 22,which is relevant to patellofemoral articulation). More informationregarding specific, enumerated definitions of nominal sizes is providedin FIG. 13B, a detailed discussion of which appears below.

Similar to the lateral condylar bulbousness illustrated in FIG. 1D, FIG.1E illustrates a comparison of bulbousness ratios defined by theportions of medial J-curves 27M corresponding to greater than 90 degreesof prosthesis flexion, shown across various prosthesis sizes as comparedto prior art devices. As illustrated, a dotted-line data set illustratesthat the medial condyles of the femoral components of the prior artZimmer NexGen CR Flex prosthesis system define a bulbousness ratio ofbetween 0.185 mm/degree (for the smallest nominal size) and 0.252mm/degree (for the largest nominal size), while the dashed-line data setillustrates the above-mentioned alternative subset of medial condyleswithin the prior art Zimmer NexGen CR Flex prosthesis system defining abulbousness ratio of between 0.209 mm/degree and 0.259 mm/degree acrossthe same range of sizes depicted in FIG. 1D. Femoral components made inaccordance with the present disclosure define a bulbousness ratio ofbetween 0.172 mm/degree (for the smallest nominal size) and 0.219mm/degree (for the largest nominal size), with each comparable size ofthe present components having a bulbousness ratio below the comparablesize of the prior art devices (as shown).

Thus, FIGS. 1D and 1E quantify the bulbous geometry for profiles 42 oflateral and medial condyles 24, 26 of cruciate-retaining type femoralcomponent 20. Similarly, FIG. 1F quantifies the corresponding bulbousJ-curve geometry for lateral and medial condyles 224, 226 ofposterior-stabilized type femoral component 220 (shown, for example, inFIG. 2A inclusive of the dashed lines and FIG. 5A) as compared to thefemoral components of the prior art Zimmer NexGen LPS Flex prosthesissystem, described above. As illustrated, a dotted-line data setillustrates that the medial and lateral condyles of the femoralcomponents of the prior art Zimmer NexGen LPS Flex prosthesis systemdefine a bulbousness ratio of between 0.209 mm/degree (for the smallestand second-smallest nominal sizes) and 0.282 mm/degree (for thesecond-largest nominal size). Femoral components made in accordance withthe present disclosure define a bulbousness ratio of between 0.208mm/degree (for the smallest nominal size) and 0.240 mm/degree (for thelargest nominal size), with each comparable size of the presentcomponents having a bulbousness ratio below the comparable size of theprior art devices (as shown).

Advantageously, the above-described bulbous geometry of condyles 24, 26,224, 226 facilitates a reduced anterior/posterior condylar thickness T(in such condyles as compared to the larger anterior/posterior condylarthickness T_(A) while also enabling high flexion (i.e., flexion of atleast 130 degrees, as noted above). For such high-flexion enablement toexist, angular sweep α must be sufficiently large such that an articularportion of J-curves is available at deep-flexion orientations. Statedanother way with reference to lateral condyle 24 shown in FIG. 1C,profile 42 of J-curve 27L must “make the turn” completely from90-degrees flexion at posterior-most point 34 through a deep flexionorientation at 130 degrees or greater.

The reduction in condylar thickness T_(C) as compared to prior artcondylar thickness T_(A) is facilitated by the bulbous geometry of theportion of J-curves 27L, 27M occupied by profile 42, which in turn flowsfrom a reduction in average radius R as compared to prior art radiusR_(A) as discussed above. More particularly, these geometrical featuresof the portions of J-curves 27L, 27M occupied by profile 42 allowJ-curves 27L, 27M to “make the turn” required in a smaller allottedanterior/posterior space. In an exemplary embodiment, the relativelygreater arc length per degree of angular sweep and smaller radius Rdefined by bulbous profile 42 allows the approximately 80-degree angularsweep α from posterior-most contact point 34 to terminal profile 44 tobe completed in a shorter anterior/posterior span, thereby allowing theoverall thickness T_(C) of condyle 24 to be reduced relative tothickness T_(A) of predicate condyle 24A.

Advantageously, this reduced condylar thickness T_(C) shifts posteriorbone contacting surface 58 posteriorly with respect to the predicateposterior bone contacting surface 58A, as illustrated in FIG. 1C, whilepreserving high-flexion enablement. Thus, femoral component 20 satisfiesan unmet need by safely allowing very deep flexion (e.g., between 130and 170 degrees) while also allowing the posterior portions of lateraland medial condyles 24, 26 to be relatively thin, thereby reducing theamount of bone that must be resected as compared to predicate devices.For example, the family of femoral component sizes provided by the priorart Zimmer CR Flex prior art designs define thickness T_(A) of between8.5 mm and 8.6 for the two smallest prosthesis sizes and in excess of 11mm for the remaining larger prosthesis sizes. An alternative prior artZimmer CR Flex prior art design, referred to in the present applicationas the “CR Flex Minus” prosthesis system, defines thickness T_(A) ofbetween 9.1 mm and 9.6 mm across the range of prosthesis sizes.

In an exemplary cruciate-retaining embodiment (FIGS. 1D and 1E), bulbousprofile 42 facilitates a condylar thickness T_(C) of 8 mm for thesmallest two prosthesis sizes and 9 mm for the remaining prosthesissizes, as measured by the maximum material thickness betweenposterior-most points 34, 36 and posterior bone-contacting surface 58.This thickness T_(C) is less than thickness T_(A) for comparableprosthesis sizes in the above-described prior art high-flexion devices.

Thus up to 2.3 mm of bone adjacent posterior bone contacting surface 58is preserved through the use of femoral component 20 as compared tocomparably-sized prior art high-flexion femoral prostheses. In anexemplary embodiment, the overall anterior/posterior space AP_(F) (FIG.1B) between anterior and posterior bone-contacting surfaces 50, 58,which corresponds to the anterior/posterior extent of the distal femurafter preparation to receive femoral component 20, is between 33 mm and56 mm. The numerical value of anterior/posterior space AP_(F) isrelatively smaller or larger in direct correspondence to the size ofcomponent 20 within a family of component sizes.

In an exemplary posterior-stabilized embodiment (FIGS. 1F and 5A),bulbous profile 42 facilitates a condylar thickness T_(C) of 9 mm forthe smallest two prosthesis sizes and 10 mm for the remaining prosthesissizes, as measured by the maximum material thickness betweenposterior-most points 34, 36 and posterior bone-contacting surface 258.This thickness T_(C) is less than thickness T_(A) for comparableprosthesis sizes in the prior art high-flexion devices. For example, afamily of prior art femoral component sizes in the Zimmer NexGen LPSFlex prosthesis system, which is a posterior-stabilized design whichenables high flexion, defines thickness T_(A) of between 10.4 mm and10.5 for the two smallest prosthesis sizes and between 12.2 mm and 12.4for the remaining larger prosthesis sizes.

Thus between 1.4 mm and 2.4 mm of bone adjacent posterior bonecontacting surface 258 is preserved through the use of femoral component220 as compared to comparably-sized prior art high-flexion femoralprostheses. In an exemplary embodiment, the overall anterior/posteriorspace AP_(F) between anterior and posterior bone-contacting surfaces250, 258, which corresponds to the anterior/posterior extent of thedistal femur after preparation to receive femoral component 220, isbetween 33 mm and 56 mm. The numerical value of anterior/posterior spaceAP_(F) is relatively smaller or larger in direct correspondence to thesize of component 220 within a family of component sizes.

2. Articular Features: “Standard” and “Narrow” Femoral Components forEach Component Size.

Turning to FIG. 3A, an anterior elevation view of regular femoralcomponent 20 is shown juxtaposed against a corresponding narrowcomponent 120. Regular component 20 includes articular geometry inaccordance with the present disclosure and adapted for a particularsubset of potential knee replacement patients, while narrow component120 has articular geometry different from component 20 and adapted for adifferent subset of patients. As best seen in FIG. 3B, femoralcomponents 20, 120 share a common sagittal geometry such that component120 is adapted to selectively mount to a femur which has been preparedto accept femoral component 20. Advantageously, this common sagittalgeometry allows a surgeon to choose intraoperatively between components20, 120.

As shown in FIG. 3B, regular femoral component 20 has five bonecontacting surfaces disposed opposite the articular surfaces of anteriorflange 22 and lateral and medial condyles 24, 26. These five bonecontacting surfaces include anterior bone contacting surface 50,anterior chamfer surface 52, distal bone contacting surface 54,posterior chamfer surface 56, and posterior bone contacting surface 58.Anterior, distal and posterior bone-contacting surfaces 50, 54, 58 areadapted to abut a resected surface of a femur upon implantation offemoral component 20. In an exemplary embodiment, anterior chamfer andposterior chamfer surfaces 52, 56 are sized and positioned to leave aslight gap between surfaces 52, 56 and the respective adjacent chamferfacet of the resected femur upon implantation, such as about 0.38 mm.However, because this gap is small and may be filled in with fixationmaterial adhering the resected chamfer facets to chamfer surfaces 52,56, anterior chamfer and posterior chamfer surfaces 52, 56 are alsoreferred to as “bone-contacting” surfaces herein.

As detailed in the Zimmer Surgical Techniques, a surgical procedure toimplant a femoral component such as component 20 includes resecting thedistal end of a femur to create five facets corresponding with bonecontacting surfaces 50, 54, 58 and chamfers 52, 56. Relatively tighttolerances between the distal end of the femur and the fivebone-contacting surfaces of femoral component 20 ensure a snug fit.

Femoral component 20 is provided in a family or kit of differingcomponent sizes, as graphically portrayed in FIGS. 3C-3F and describedin detail below. Consideration in choosing an appropriately sizedfemoral component 20 from among the set of components include the amountof bone resection necessary to accommodate the component 20, and theability for resected surfaces to make full-area, flush contact with theadjacent bone-contacting surfaces 50, 52, 54, 56, 58 of femoralcomponent 20 (see, e.g., FIG. 11B showing femoral component 220implanted upon femur F). To implant femoral component 20, theanterior/posterior distance defined by the anterior and posterior facetsof the resected femur must match the corresponding anterior/posteriordistance AP_(F) (FIG. 1B) between anterior bone contacting surface 50and posterior bone contacting surface 58. An appropriately sized femoralcomponent 20 provides snug abutting contact between all five of thebone-contacting surfaces of femoral component 20 and the distal resectedfacets, while also resulting in a desired articular profile in the kneeprosthesis.

In the interest of preserving as much natural bone stock as practical,it is desirable to maximize the anterior/posterior distance AP_(F) offemoral component 20 provided the articular profile is acceptable to thesurgeon. However, no two patients are exactly alike. In some cases, forexample, the overall sagittal geometry of bone contacting surfaces 50,54, 58 and chamfers 52, 56 may represent an ideal match for the femur ofa particular patient, but the peripheral characteristics of femoralcomponent 20 (described in detail below) may not present an adequatematch to the other anatomical features of the femur. The presentdisclosure addresses this eventuality by providing alternative femoralcomponent designs sharing a common sagittal geometry, as illustrated inFIG. 3B.

For example, the height H_(SF) and geometry of anterior flange 22 ofregular femoral component 20 (FIGS. 3A, 3B and 3D) may result in“overhang” thereof past the associated anterior facet of the resectedfemur. Similarly, the overall medial/lateral width ML_(S) of regularfemoral component 20 (FIGS. 3A and 3C) may be too large, as indicated byoverhang of one or more bone-contacting surfaces 50, 52, 54, 56, 58 pastthe medial and/or lateral edge of the patient's femur. Yet anotherpossibility is that the overall proximal/distal heights H_(SM), H_(SL)of medial and lateral condyles 26, 24, respectively (FIGS. 3A, 3B, 3E,and 3F) may be too large, also potentially resulting in overhang of thecomponent beyond the resected posterior facets of the femur. In each ofthese cases, femoral component 20 would normally be considered toolarge, possibly resulting in the use of a smaller component size withits associate reduction in anterior/posterior distance AP_(F) (FIGS. 1Band 3B).

Moreover, Applicants have found that for a substantial subset of kneereplacement candidates, “regular” or standard femoral component sizesmay have an appropriate anterior/posterior distance AP_(F) and spatialarrangement of bone contacting surfaces 50, 54, 58 and chamfers 52, 56,but are too large with respect to one or more of the aforementionedcharacteristics of the component periphery, and usually all three (i.e.,height H_(SF) and geometry of anterior flange 22, overall width ML_(S),and condyle heights H_(SM), H_(SL)).

To accommodate a wider variety of femoral geometries while facilitatingmaximum preservation of healthy bone stock during the surgicalprocedure, a prosthesis system in accordance with the present disclosureprovides a set of “narrow” femoral components 120 which share a commonspatial arrangement of bone contacting surface geometry with acorresponding set of femoral components 20 (i.e., a commonanterior/posterior distance AP_(F) and associated sagittal profile ofresected facets), but includes anterior flange 122, lateral condyle 124and medial condyle 126 which are strategically downsized.

In the anterior elevation view of FIG. 3A, the periphery of narrowfemoral component 120 is aligned with the periphery of regular femoralcomponent 20 such that lateral distal-most contact points 30, 130 andmedial distal-most contact points 32, 132 are superimposed over oneanother. Moreover, the articular profile and geometry of condyles 24, 26of femoral component 20, including medial and lateral J-curves 27M, 27Ldescribed above (FIG. 3B), are substantially identical to thecorresponding profile of condyles 124, 126 of narrow femoral component120, with the exception of the reduction in various peripheral aspectsof femoral component 120 as compared to component 20 as described below.Taking account of such reductions, the articular surfaces of femoralcomponent 120 are subsumed by the articular surfaces of femoralcomponent 20 when the articular surfaces of components 20, 120 aresuperimposed, as illustrated in FIGS. 3A and 3B. Thus, both of femoralcomponents 20 and 120 may be used interchangeably with a selectedabutting tibial component, such as tibial bearing component 240 (FIG.6).

However, anterior flange 122 of narrow femoral component 120 defines ashorter overall flange height H_(CF), as illustrated in FIGS. 3A, 3B and3D. In an exemplary embodiment, height H_(CF) may be reduced by 1 mmfrom the corresponding height H_(SF) of anterior flange 22 of regularfemoral component 20 for any given prosthesis size. As shown in FIG. 3D,height H_(SF) of femoral component 20 ranges from 38 mm to 51 mm, andgrows progressively larger across a range of prosthesis sizes (startingfrom a nominal size 3 and ending at a nominal size 12). By contrast,height H_(CF) of femoral component 120 ranges from 35 mm to 47 across anoverlapping range of prosthesis sizes (starting from a nominal size 1and ending at a nominal size 11). As illustrated in the lines connectingthe data points of FIG. 3D, anterior flange heights H_(CF) of each sizeof femoral component 120 are consistently less than the correspondingflange heights H_(SF) for corresponding sizes of femoral component 20. Acommon nominal size for femoral components 20, 120 denotes asubstantially identical spatial arrangement of bone contacting surfacegeometry, including a common anterior/posterior distance AP_(F), suchthat either of a particular size of component 20, 120 can be implantedonto the same resected femur.

Medial condyle height H_(CM) of medial condyle 126 is also shorter thanthe corresponding medial condyle height H_(SM) of standard medialcondyle 26. In an exemplary embodiment, height H_(CM) may be reduced by1 mm from the corresponding height H_(SM) of medial condyle 26 ofregular femoral component 20 for any given prosthesis size. As shown inFIG. 3F, height H_(SM) of medial condyle 26 of regular femoral component20 ranges from 24 mm to 33 mm, and grows progressively larger across arange of prosthesis sizes (starting from a nominal size 3 and ending ata nominal size 12). By contrast, height H_(CM) of femoral component 120ranges from 21 mm to 31 mm across an overlapping range of prosthesissizes (starting from a nominal size 1 and ending at a nominal size 11).As illustrated in the lines connecting the data points of FIG. 3F,medial condyle heights H_(CM) of femoral component 120 are consistentlyless than the corresponding medial condyle heights H_(SM) of femoralcomponent 20 across a range of corresponding sizes.

Similarly, lateral condyle height H_(CL) of lateral condyle 124 is lessthan lateral condyle height H_(SL) of lateral condyle 24. In anexemplary embodiment, height H_(CL) may be reduced by 1 mm from thecorresponding height H_(SL) of lateral condyle 24 of regular femoralcomponent 20 for any given prosthesis size. As shown in FIG. 3E, heightH_(SL) of lateral condyle 24 of regular femoral component 20 ranges from22 mm to 31 mm, and grows progressively larger across a range ofprosthesis sizes (starting from a nominal size 3 and ending at a nominalsize 12). By contrast, height H_(CL) of lateral condyle 124 of femoralcomponent 120 ranges from 19 mm to 29 mm across an overlapping range ofprosthesis sizes (starting from a nominal size 1 and ending at a nominalsize 11). As illustrated in the lines connecting the data points of FIG.3E, lateral condyle heights H_(CL) of femoral component 120 areconsistently less than the corresponding lateral condyle heights H_(SL)of femoral component 20 across a range of corresponding sizes.

Referring now to FIG. 3A, the overall width ML_(C) of narrow femoralcomponent 120 is also consistently less than the overall width ML_(S) offemoral component 20 across a range of prosthesis sizes. In an exemplaryembodiment, width ML_(C) may be reduced by between 1 mm from thecorresponding width ML_(S) of regular femoral component 20 for any givenprosthesis size. As shown in FIG. 3C, width ML_(S) of regular femoralcomponent 20 ranges from 62 mm to 78 mm, and grows progressively largeracross a range of prosthesis sizes (starting from a nominal size 3 andending at a nominal size 12). By contrast, width ML_(C) of femoralcomponent 120 ranges from 55 mm to 70 mm across an overlapping range ofprosthesis sizes (starting from a nominal size 1 and ending at a nominalsize 11). As illustrated in the lines connecting the data points of FIG.3C, width ML_(C) of femoral component 120 is consistently less than thecorresponding width ML_(S) of femoral component 20 across each size in arange of corresponding sizes.

The above-described changes in peripheral characteristics to femoralcomponent 120, as compared to femoral component 20, advantageously leavethe overall sagittal profile of components 20, 120 similar, and withsubstantially identical anterior/posterior spaces between anteriorbone-contacting surfaces 50, 150 and posterior bone-contacting surfaces58, 158 (including distance AP_(F)). However, it is appreciated that theshortening of anterior flange 122 and posterior condyles 124, 126 doalter the sagittal profile of component 120 in that such profile is“shortened” overall. However, the sagittal profile of component 120 issubsumed by the corresponding profile of regular component 20 (asillustrated in FIG. 3B), such that narrow component 120 will fit thesame resected femur as component 20. Advantageously, this shorteningprevents potential overhang of component 120 past the resected portionsof some femurs, as discussed above.

In addition to the differences in the peripheral characteristicsdescribed above, articular features of anterior flange 122 also vary ascompared to anterior flange 22 of regular femoral component 20.Referring to FIG. 3A, standard anterior flange 22 defines flange taperangle s, which is the taper angle defined by the medial and lateralwalls adjoining anterior bone-contacting surface 50 to the opposedarticular surface of flange 22. In the illustrative embodiment of FIG.3A, taper angle β_(S) angle is measured between lines tangent to pointsalong the rounded frontal profile defined by the medial and lateralwalls of anterior flange 22 at the base of anterior bone-contactingsurface 50 (i.e., where anterior bone-contacting surface 50 meetsanterior chamfer surface 52). However, it is appreciated that taperangle β_(S) may be defined at any point along such rounded edges,provided the medial and lateral tangent lines are drawn at commonproximal/distal heights for purposes of comparison between femoralcomponents 20, 120.

In contrast to standard anterior flange 22, narrow anterior flange 122defines taper angle β_(C) which is different from taper angle β_(S) forany given nominal prosthesis size. This disparity of taper anglesfacilitates a relatively smaller disparity in overall heights H_(SF),H_(CF) of anterior flanges 22, 122 as compared to the relatively largerdisparity in overall widths ML_(C), ML_(S) thereof (as shown bycomparison of FIGS. 3C and 3D, and detailed above). Advantageously, thisdiffering taper defined by taper angles β_(S), β_(C) in anterior flanges22, 122 accommodates a wide range of natural patient anatomies forlarger- and smaller-stature patients.

Yet another difference between regular femoral component 20 and narrowfemoral component 120 is the angle defined by patellar grooves 60, 160(also referred to a patellar sulcus) formed in anterior flanges 22, 122respectively. As best illustrated in FIG. 8, anterior flange 22 definespatellar groove 60, which is a longitudinal concavity or troughextending along the proximal/distal extent of anterior flange 22, asshown in FIG. 3A. A natural or prosthetic patella articulates withgroove 60 during normal flexion and extension of the knee. Turning backto FIG. 3A, the path of the deepest portion of the patellar troughdefined by patellar groove 60 is represented by the illustrated sulcusaxis, which is extrapolated proximally and distally for clarity. Thesulcus axis of patellar groove 60 defines angle γ_(S) with a transverseplane tangent to distal most points 30, 32 of lateral and medialcondyles 24, 26. In the illustrated embodiment of FIG. 3A, thistransverse plane appears as an imaginary line connecting distal-mostpoints 30, 32 (and also, therefore, connecting distal-most points 130,132 of the superimposed narrow femoral component 120).

As illustrated, standard patellar groove angle γ_(S) is greater than thecorresponding groove angle γ_(C) defined by patellar groove 160 ofanterior flange 122. In an exemplary embodiment, standard patellargroove angle γ_(S) is 83 degrees, while the narrow-component patellargroove angle γ_(C) is 80 degrees.

It is contemplated that for each regular femoral component size withinthe range of available sizes (i.e., for a range of unique, differinganterior distances AP_(F)), one narrow femoral component including thefeatures described above may be provided. In an exemplary embodiment, upto twelve or more unique femoral component sizes may be provided, witheach of the 12 sizes including both regular and narrow femoralcomponents 20, 120. Thus, a surgeon may intraoperatively elect toimplant narrow femoral component 120 if it becomes apparent that regularfemoral component 20 is too large in certain respects (as describedabove).

An exemplary surgical technique and apparatus for intraoperativelychoosing between regular femoral component 20 and narrow femoralcomponent 120 is described in U.S. patent application Ser. No.13/161,624, filed Jun. 16, 2011 and entitled FEMORAL PROSTHESIS SYSTEM(Attorney Docket No. ZIM0896), the entire disclosure of which is herebyexpressly incorporated herein by reference.

However, it is also contemplated that multiple narrow components may beprovided corresponding to each standard component size. Each of theplurality of narrow components may feature different widths, heightsand/or anterior flange arrangements in accordance with the principlesdescribed above.

3. Articular Features: Differential Condyle Height.

Referring again to FIG. 1C, medial condyle 26 is taller (i.e., defines agreater proximal/distal extent) as compared to lateral condyle 24 todefine height differential ΔH. In an exemplary embodiment, heightdifferential ΔH may be between 1.1 and 2.3 mm depending on prosthesissize. As described in detail below, an exemplary family or set offemoral components 20 may include twelve prosthesis sizes, with thesmallest size defining height differential ΔH at 1.1 mm and the largestsize defining height differential ΔH at 2.3 mm. Intermediate sizesdefine intermediate height differentials ΔH within the aforementionedrange.

In an exemplary embodiment, each adjacent pair of prosthesis sizes haverespective height differentials ΔH that vary by 0.1 mm, with largersizes having proportionally larger variance in height differentials ΔH.Thus, for example, a prosthesis having a nominal size of 1 may have aheight differential ΔH of 1.1 mm, while a prosthesis having nominal size2 has a height differential ΔH of 1.2 mm.

By contrast, the femoral components of the prior art Zimmer NexGen CRFlex prosthesis system have medial condyles which are taller than thelateral condyles by between 1.3 mm and 2.1 mm. Further, families offemoral components of the prior art Zimmer NexGen CR Flex prosthesissystem have variability in the condyle height differential which do notgrow proportionally larger as nominal sizes increase, instead havingdifferentials which grow at varying rates across the range of sizes.

Advantageously, providing a relatively shorter lateral condyle 24 allowssuch lateral condyle 24 to roll back and externally rotate when the kneeprosthesis is in deep flexion (FIG. 2A). This deep-flexion rollback androtation is permitted by shortened lateral condyle 24, while anypotential impingement between condyle 24 and adjacent structures and/orsoft tissues is avoided. This facilitation of femoral roll back isparticularly effective in combination with the other features of acruciate-retaining femoral component, such as component 20, which lacksa femoral cam as described herein.

4. Soft Tissue Accommodation: Femoral Cam Geometry.

Turning now to FIG. 5A, posterior stabilized (PS) femoral component 220having femoral cam 276 is illustrated. Femoral component 220 issubstantially similar to femoral component 20 described above, withreference numerals of component 220 corresponding to the referencenumerals used in component 20, except with 200 added thereto. Structuresof femoral component 220 correspond to similar structures denoted bycorresponding reference numerals of femoral component 20, except asotherwise noted.

However, femoral component 220 is specifically adapted for use in asurgical procedure wherein the posterior cruciate ligament (PCL) isresected. More particularly, femoral component 220 includes femoral cam276 spanning intercondylar notch 268 formed between lateral and medialcondyles 224, 226. Intercondylar notch 268 is bounded at its lateral andmedial sides by lateral and medial condylar walls 238, 239 (FIG. 5C),which face inwardly toward one another and each extend proximally fromdistal bone-contacting surface 254. Condylar walls 238, 239 areengageable with spine 278 of tibial bearing component 240 (FIG. 6) toprovide medial/lateral stability to femoral component 220 from fullextension to at least mid-flexion; therefore, in an exemplary embodimentcondylar walls 238, 239 are substantially parallel to one another todefine a total medial/lateral width ML_(T) which remains constant acrossthe anterior/posterior extent of intercondylar notch 268.

Femoral cam 276 is sized, shaped and positioned to articulate with spine278 of tibial bearing component 240 (FIG. 6) along posterior articularsurface 280 thereof (as described in detail below). Spine 278 extendsproximally from the articular surface of tibial bearing component 240,and is disposed between lateral and medial articular compartments 246,248 thereof. Additional details of spine 278 and its interaction withfemoral cam 276 are described in: U.S. Provisional Patent ApplicationSer. No. 61/561,657, filed Nov. 18, 2011 and entitled “TIBIAL BEARINGCOMPONENT FOR A KNEE PROSTHESIS WITH IMPROVED ARTICULAR CHARACTERISTICS”(Attorney Docket ZIM0912); U.S. Provisional Patent Application Ser. No.61/577,293, filed Dec. 19, 2011 and entitled “TIBIAL BEARING COMPONENTFOR A KNEE PROSTHESIS WITH IMPROVED ARTICULAR CHARACTERISTICS” (AttorneyDocket ZIM0912-01); U.S. Provisional Patent Application Ser. No.61/592,576, filed Jan. 30, 2012 and entitled “TIBIAL BEARING COMPONENTFOR A KNEE PROSTHESIS WITH IMPROVED ARTICULAR CHARACTERISTICS” (AttorneyDocket ZIM0912-02); U.S. Provisional Patent Application Ser. No. ______,filed on even date herewith and entitled “TIBIAL BEARING COMPONENT FOR AKNEE PROSTHESIS WITH IMPROVED ARTICULAR CHARACTERISTICS” (AttorneyDocket ZIM0912-03); and U.S. Provisional Patent Application Ser. No.______, filed on even date herewith and entitled “TIBIAL BEARINGCOMPONENT FOR A KNEE PROSTHESIS WITH IMPROVED ARTICULAR CHARACTERISTICS”(Attorney Docket ZIM0912-04). The entire disclosures of each of theabove-identified patent applications are hereby expressly incorporatedherein by reference.

Femoral cam 276 includes central articular area 282 defined by aplurality of cylindrical surfaces tangent to one another, with thelongitudinal axes defined by such cylindrical surfaces all substantiallyparallel to one another and extending in a medial/lateral direction.Central articular area 282 is flanked by medial and lateral transitionareas 284M, 284L which provide a rounded transition from the cylindricalcentral articular area to lateral and medial condyles 224, 226, as shownin FIG. 5A and described in detail below.

More particularly, FIG. 5B illustrates four cylindrical surface curves286, 288, 290, 292 as viewed in a sagittal cross-section bisectingfemoral cam 276. As described in detail below, curves 286, 288, 290, 292are indicative of surfaces when viewed from a perspective other than thesagittal perspective of FIG. 5B. Proximal curve 286 extends posteriorlyfrom posterior bone contacting surface 258, and defines a relativelylarge curvature radius R₁. In an exemplary embodiment, radius R₁ may beas little as 10 mm or as large as 11.5 mm, with larger values for radiusR₁ corresponding to larger prosthesis sizes within a family of differentprosthesis sizes.

Posterior curve 288 tangentially adjoins proximal curve 286, therebycreating a smooth transition between curves 286, 288. As viewed from thesagittal perspective of FIG. 5B, posterior curve 288 extends posteriorlyand distally from its junction with proximal curve 286. Posterior curve288 defines radius R₂ which is smaller than radius R₁. In an exemplaryembodiment, radius R₂ may be as little as 2.5 mm, 6.5 mm or 7 mm andlarge as 8 mm or 12 mm, or may be any size within any range defined bythe foregoing values. Similar to radius R₁ discussed above, largervalues of radius R₁ may correspond to larger prosthesis sizes within afamily of prostheses.

Distal curve 290 tangentially adjoins posterior curve 288 to createanother smooth transition between curves 288, 290. As viewed from thesagittal perspective of FIG. 5B, distal curve 290 extends distally andanteriorly from its junction with posterior curve 288. Distal curve 290defines radius R₃ which is smaller than radius R₂ of posterior curve288. In an exemplary embodiment, radius R₃ may be between 2 mm and 3 mmacross all sizes in the aforementioned family of prostheses.

Anterior curve 292 tangentially adjoins distal curve 290, and extendsanteriorly and proximally therefrom, to rejoin posterior bone contactingsurface 258. Anterior curve 292 defines a very large radius, or issubstantially flat. As noted above, curves 286, 288, 290 each define amedially/laterally extending cylindrical face, such that centers C₁, C₂,C₃ of radii R₁, R₂, R₃, respectively, lie on respectivemedially/laterally extending longitudinal cylinder axes. Stated anotherway, the cylindrical faces and longitudinal axes of curves 286, 288, 290extend into and out of the page of FIG. 5B.

Although the sagittal curve arrangement described above utilizes threearticular curves to define central articular area 282, it iscontemplated that any number of mutually tangent curves may be used. Forexample, in certain exemplary embodiments posterior curve 288 may bebroken up into two sections, in which a transitional curve portionbetween radii R₁, R₂ has a relatively smaller radius than either ofradii R₁, R₂, thereby providing a decisive transition from themid-flexion articular characteristics provided by posterior curve 288(as described below) and the deep-flexion articular characteristics ofproximal curve 286 (also described below).

As described above with regard to the exemplary embodiment of femoralcomponent 220, the articular surfaces defined by curves 286, 288, 290are shown and described as cylindrical and therefore are depicted asstraight lines in the coronal cross-section of FIG. 5C. However, it iscontemplated that central articular area 282 may have a slightmedial/lateral curvature, such as a slight convex curvature resulting ina slightly curved coronal profile. Moreover, for purposes of the presentdisclosure, a geometric shape defined by a component of a kneeprosthesis (such as a cylindrical surface) refers to a shape having thenominal characteristics of that geometric shape, it being appreciatedthat manufacturing tolerances and circumstances of in vivo use may causesuch nominal characteristics to deviate slightly.

Turning now to FIG. 5C, the cylindrical surfaces including curves 286,288, 290 define varying medial/lateral extents along the respectivelongitudinal axes defined by the curves. As described in detail below,these varying axial extents cooperate to accommodate the unique demandson central articular area 282 through the range of prosthesis flexion.

Medial/lateral extent ML_(P) is defined by proximal cylindrical surface286, which corresponds to a deep-flexion portion of central articulararea 282, i.e., that part of femoral cam 276 which contacts spine 278during deep flexion of femoral component 220. In the context of thevarying widths defined by central articular area 282, medial/lateralextent ML_(P) is relatively small. In an exemplary embodiment,medial/lateral extent ML_(P) may be as small as 1.5 mm or 3 mm, and maybe as large as 3.5 mm or 5 mm, or may be any size within any rangedefined by the foregoing values. For example, in an exemplary family offemoral components having different component sizes, medial/lateralextent ML_(P) may grow larger as the component sizes increase. In thisexemplary family of components, medial/lateral extent ML_(P) is between10% and 25% of total intercondylar width ML-r, which in turn ranges from14 mm to 22 mm.

By contrast, medial/lateral extent ML_(D) is defined by distalcylindrical surface 290, which corresponds to an initial-flexion portionof central articular area 282. Medial/lateral extent ML_(D) of distalcylindrical surface 290 is relatively larger than medial/lateral extentML_(P), and represents the largest medial/lateral extent of centralarticular area 282. In an exemplary embodiment, medial/lateral extentML_(D) may be as small as 12 mm, 14.8 mm or 15 mm, and may be as largeas 16.1 mm, 19.5 mm or 20 mm, or may be any size within any rangedefined by the foregoing values. As best seen in FIG. 5A, posteriorcylindrical surface 288 defines a steadily expanding medial/lateralextent which smoothly transitions from the narrower proximalmedial/lateral extent ML_(P) to the wider distal medial/lateral extentML_(D). For example, in the above-mentioned exemplary family of femoralcomponents having different component sizes, medial/lateral extentML_(D) may grow larger as the component sizes increase. In thisexemplary family of components, medial/lateral extent ML_(D) is between85% and 95% of total intercondylar width ML_(T).

Lateral and medial transition areas 284L, 284M (FIG. 5C) flank centralarticular area 282 and extend laterally and medially to join articulararea 282 to the adjacent lateral and medial condyles 224, 226,respectively. In an exemplary embodiment, medial and lateral transitionareas 284M, 284L are mirror images of one another about a sagittalplane, i.e., the section plane of FIG. 5B which is parallel to andequidistant from lateral and medial condylar walls 238, 239. However, itis contemplated that differing transition areas may be employed asrequired or desired for a particular application.

Transition areas 284M, 284L define transition surfaces corresponding tothe respective central articular surfaces to which they are adjoined.For example, FIG. 5C illustrates a representative coronal cross-sectionof femoral cam 276, in which the curvature of transitions areas 284M,284L is depicted. Convex lateral and medial transition surfaces definingcoronal radius R₄ flank the lateral and medial terminus of proximalcentral articular surface 286, forming a tangent with surface 286 andextending medially and laterally toward lateral and medial condyles 224,226 respectively. In an exemplary embodiment, radius R₄ may be as smallas 6 mm, 6.5 mm or 7 mm, and may be as large as 8 mm or 12 mm, or may beany size within any range defined by the foregoing values. In anexemplary family of prosthesis sizes, larger values for radius R₄correspond to larger prosthesis sizes. Across all sizes, however, radiusR₄ represents a significant portion of the total medial/lateral widthML_(T). For example, radius R₄ may be equal to as little as 40%, 41% or44% of total medial/lateral width ML_(T), or may be as large as 46% or56% thereof, or may be any percentage within any range defined by theforegoing values.

Referring still to FIG. 5C, the widely radiused and convex coronalcurvature defined by radius R₄ gives way to a tighter concave curvaturehaving radius R₅ as lateral and medial transitional areas 284L, 284Mapproach intersection with lateral and medial condyles 224, 226respectively. This concave curvature is tangent to radius R₄ and to theadjacent surfaces of condyles 224, 226, thereby forming a smoothtransition therebetween. Similarly, the portion of transition areas284L, 284M which join distal and anterior surfaces 290, 292 (FIG. 5B) offemoral cam 276 to condyles 224, 226 are composed only of concavecurvature having radius R₆, owing to the substantial width of surfaces290, 292 (as discussed above). In an exemplary embodiment, both radiusR₅ and radius R₆ are at least 1 mm. As noted above, all other radiidefined by the surfaces of femoral cam 276 are substantially larger than1 mm. Thus, femoral cam 276 defines a minimum radius of at least 1 mm atall parts subject to articulation with any adjacent soft tissues orprosthesis structures (i.e., excluding the portion of posteriorbone-contacting surface 258, which only abuts the corresponding facet ofthe bone after implantation).

Moreover, the concave transitional radii R₅, R₆ are not generallyconsidered a portion of the “articular” surfaces of femoral cam 276,because these concave surfaces will not come into contact with spine 278of tibial bearing component 240 (FIG. 6). Rather, central articular area282 and lateral and medial transitional areas 284L, 284M form thepotential articular surfaces with regard to spine 278, and these areascombine to occupy a large proportion of total medial/lateral widthML_(T). In an exemplary embodiment, the overall portion of totalmedial/lateral width ML_(T) occupied by the combination of centralarticular area 282 and the convex portions of transition areas 284L,284M is as little as 80%, 85% or 88%, and as much as 89% or 91%, or maybe any percentage within any range defined by the foregoing values.Thus, only surfaces which are broadly convex and/or cylindrical arepresented to surrounding tissues and anatomical structures, therebymaximizing surface area contact (and reducing contact pressure) betweenfemoral cam 276 and spine 278 during articulation.

As illustrated in FIGS. 5A and 5B, femoral cam 276 is disposed betweenlateral and medial condyles 224, 226 near the proximal-most portionthereof. In use, the relative positioning of femoral cam 276 and tibialspine 278 results in initial contact therebetween in mid-flexion. Asfemoral component 220 as articulates with tibial bearing component 240through the range of flexion, a portion of distal curve 290 initiallycontacts spine 278 along proximal contact line 294 (FIG. 6). In anexemplary embodiment, this initial contact occurs at a prosthesisflexion angle θ (FIG. 2A) of between 75 degrees and 93 degrees. In thismid-flexion configuration, external rotation of femoral component 220has not yet begun, and the wide medial/lateral extent ML_(D)) of thecylindrical distal surface 290 is in articular contact with a comparablywide medial/lateral extent of proximal contact line 294 to provide alarge contact area and associated low contact pressure.

As femoral component 220 transitions into deeper flexion orientations(i.e., larger flexion angles θ as shown in FIG. 2A), contact betweenfemoral cam 276 and posterior articular surface 280 of spine 278 movesdistally toward distal contact line 296 (FIG. 6). Simultaneously, thecontact area on cam 276 transitions from distal surface 290, throughposterior surface 288, and ultimately to proximal surface 286 once indeep flexion (e.g., when angle θ approaches and surpasses 155 degrees,as shown in FIG. 2A). In deep flexion, femoral component 220 alsoexternally rotates, thereby altering the orientation of cylindricalsurfaces 286, 288, 290 of femoral cam 276 with respect to posteriorarticular surface 280 of spine 278. To accommodate this alteredorientation, posterior articular surface 280 angles or “turns” as cam276 moves from proximal contact line 294 toward distal contact line 296.Thus, the anterior/posterior thickness defined by spine 278 along distalcontact line 296 is greater near lateral articular compartment 246 ascompared to the corresponding thickness near medial articularcompartment 248.

This configuration of posterior articular surface 280 and attendantchange in thickness is described in detail in: U.S. Provisional PatentApplication Ser. No. 61/561,657, filed Nov. 18, 2011 and entitled“TIBIAL BEARING COMPONENT FOR A KNEE PROSTHESIS WITH IMPROVED ARTICULARCHARACTERISTICS” (Attorney Docket ZIM0912); U.S. Provisional PatentApplication Ser. No. 61/577,293, filed Dec. 19, 2011 and entitled“TIBIAL BEARING COMPONENT FOR A KNEE PROSTHESIS WITH IMPROVED ARTICULARCHARACTERISTICS” (Attorney Docket ZIM0912-01); U.S. Provisional PatentApplication Ser. No. 61/592,576, filed Jan. 30, 2012 and entitled“TIBIAL BEARING COMPONENT FOR A KNEE PROSTHESIS WITH IMPROVED ARTICULARCHARACTERISTICS” (Attorney Docket ZIM0912-02); U.S. Provisional PatentApplication Ser. No. ______, filed on even date herewith and entitled“TIBIAL BEARING COMPONENT FOR A KNEE PROSTHESIS WITH IMPROVED ARTICULARCHARACTERISTICS” (Attorney Docket ZIM0912-03); and U.S. ProvisionalPatent Application Ser. No. ______, filed on even date herewith andentitled “TIBIAL BEARING COMPONENT FOR A KNEE PROSTHESIS WITH IMPROVEDARTICULAR CHARACTERISTICS” (Attorney Docket ZIM0912-04). The entiredisclosures of each of the above-identified patent applications arehereby expressly incorporated herein by reference.

As external rotation of femoral component 220 initiates in deep flexion,engagement of posterior articular surface 280 of spine 278 shifts fromdistal surface 290 to posterior surface 288 of cam 276. As this shifttakes place, the convex portions of transition areas 284M, 284L(described in detail above) move into position near the medial andlateral edges of posterior articular surface 280. As flexion (andexternal rotation) of femoral component 220 progresses, contact betweenfemoral cam 276 and posterior articular surface 280 transitions fromposterior surface 288 and to proximal surface 286. Proximal surface 286defines a smaller medial/lateral width ML_(P) compared to width ML_(D)of distal surface 290 creating the medial/lateral space for thelarge-radius, broadly convex portions of transition areas 284M, 284Lflanking proximal surface 286 (FIG. 5A). These large portions oftransition areas 284M, 284L facilitate solid contact between therelatively narrower proximal surface 286 when femoral component 220internally or externally rotates in deep flexion, thereby ensuring thata large area of contact and concomitantly low contact pressure betweenfemoral cam 276 and tibial spine 278 is maintained.

Stated another way, the potential for internal/external rotation offemoral component 220 increases with increasingly deep flexion. Suchinternal/external rotation also causes the longitudinal axis of femoralcam 276 to rotate with respect to posterior surface 280 of tibial spine278, thereby potentially misaligning one of cylindrical surfaces 286,288 with posterior surface 280 (depending on the level of flexion). Thismisalignment is accommodated by the progressive narrowing of cylindricalsurface 288 (and resulting narrow width ML_(P) of proximal surface 286),which concomitantly increases the medial/lateral extent of transitionareas 284M, 284L. The narrower cylindrical surfaces 286, 288 present asmaller area of contact with posterior surface 280 of spine 278, whichin turn allows femoral cam 276 the requisite rotational freedom toaccommodate internal/external rotation while maintaining area contactbetween the cylindrical surface of proximal surface 286 of femoral camand the angled distal contact line 296 along posterior surface 280 ofspine 278.

Advantageously, medial and lateral transition areas 284M, 284L provide aspace or “trough” that is strategically located to accommodate the edgesof spine 278 adjacent posterior articular surface 280, as femoralcomponent 220 rotates externally and/or internally. This accommodationprevents any potential for impingement of cam 276 upon spine 278 in deepflexion. At the same time, radii R₄ are relatively large, therebyproviding a widely rounded, convex and “soft tissue friendly” surface toreduce contact pressure in the event of soft tissue impingement upontransition areas 284L, 284M. Convex radii R₅ similarly eliminate anysharp edges in the vicinity of femoral cam 276, further minimizingpotential contact pressures caused by impingements thereupon.

By contrast, predicate femoral components utilize an articular surfacethat is concave along its medial/lateral extent, and includes transitionarea radii that are substantially less than 1 mm. One such prior artfemoral component forms a part of the NexGen LPS Flex prosthesis system(described above).

5. Soft Tissue Accommodation: Asymmetric Intercondylar Notch.

Referring to FIG. 7, for cruciate retaining (CR) femoral componentdesigns, such as femoral component 20, intercondylar notch 68 islaterally and medially bounded by lateral inner sidewall 76 and medialinner sidewall 77, respectively. As described in detail below, innersidewalls 76, 77 define angular orientations with respect to femoralcomponent 20 which operate to protect the posterior cruciate ligament(PCL) during prosthesis articulation. As noted above, the PCL isretained in the surgical procedure implanting cruciate retaining femoralcomponent 20 and associated prosthesis components.

Referring to FIG. 7, femoral component 20 defines bisecting axis 80,which divides femoral component 20 into medial and lateral halves. Inthe context of component 20, bisecting axis 80 bisects the arcuateanterior terminus 82 of intercondylar notch 68, and is perpendicular toa posterior coronal plane defined by posterior bone contacting surface58. However, it is contemplated that bisecting axis 80 may be defined ina number of other ways, provided that axis 80 generally divides afemoral component made in accordance with the present disclosure intomedial and lateral halves. In the context of patient anatomy, bisectingaxis 80 corresponds to Whiteside's line when implanted onto a femur.Whiteside's line is defined as the line joining the deepest part of theanatomic patellar groove, anteriorly, and the center of the anatomicintercondylar notch, posteriorly.

Lateral inner sidewall 76 defines angle σ_(L) with respect to bisectingaxis 80, while medial sidewall 77 defines angle σ_(M) with respect tobisecting axis 80. Intercondylar notch 68 may be said to be “asymmetric”because medial sidewall angle σ_(M) is greater than lateral sidewallangle σ_(L). Advantageously, this asymmetric angular arrangement ofsidewalls 76, 77 of intercondylar notch 68 facilitates external rotationof femoral component 20 in deep flexion (described in detail above) byproviding additional space for the posterior cruciate ligament on themedial side. This additional medial space avoids potential contactbetween the PCL and medial inner sidewall 77 which might otherwise occurwhen femoral component 20 externally rotates.

6. Soft Tissue Accommodation: Rounded Anterior Flange.

FIG. 8 illustrates a cross-section of anterior flange 22 of femoralcomponent 20. As illustrated in FIG. 1B, the cross-sectional profile ofFIG. 8 is taken at the junction of anterior bone-contacting surface 50and anterior chamfer surface 52 (and through the middle of thicknessridge 300, as described below). The plane of the FIG. 8 cross section istaken generally perpendicular to the adjacent surfaces, i.e., such thatthe minimum material thicknesses are shown. For simplicity, thegeometric features of anterior flange 22 are described with reference tothe cross section of FIG. 8, it being understood that such geometricfeatures also propagate through the remainder of anterior flange 22.

As shown in FIG. 8, anterior flange 22 includes lateral condylar portion62 and medial condylar portion 63, with a concave patellar groove 60disposed therebetween. As noted above, a natural or prosthetic patellaarticulates with the concave patellar groove 60 during prosthesisarticulation. During such articulation, lateral and medial condylarportions 62, 63 provide constraint to medial and lateral movement of thepatella. The level of medial/lateral constraint depends in part on “jumpheights” JH_(L), JH_(M), defined by condylar portions 62, 63. Jumpheights JH_(L), JH_(M), illustrated in FIG. 8, represent the amount ofanterior travel, i.e., travel outwardly away from patellar groove 60,that a patella would have to traverse in order for subluxation of thepatella component from the lateral and medial sides of anterior flange22, respectively to occur. In anterior flange 22, jump heights JH_(L),JH_(M) are arranged to prevent such subluxation under normal operatingconditions of the prosthesis. In an exemplary embodiment, medial jumpheight JH_(M) is between 3.0 mm and 4.6 mm and lateral jump heightJH_(L) is between 3.5 mm and 5.7 mm. These jump height value ranges arecomparable to the prior art femoral components of the Zimmer NexGenprosthesis series, e.g., the NexGen CR Flex prosthesis system and theNexGen LPS Flex prosthesis system.

Anterior flange 22 defines large-radius, convex lateral and medialcondylar portions 62, 63 respectively. Lateral edge 98 extends from peak62P of the convex lateral condylar portion 62, to the lateral edge ofanterior bone contacting surface 50. Similarly, medial edge 99 extendsfrom peak 63P of the convex medial condylar portion 63 to the medialedge of anterior bone contacting surface 50. Peaks 62P, 63P cooperatewith patellar groove 60 to define lateral jump height JH_(L), JH_(M)respectively, as illustrated in FIG. 8. As compared with alternativeanterior flange profiles (schematically illustrated in FIG. 8 usingdashed lines), anterior flange 22 includes lateral and medial edges 98,99 which define larger radii of curvature R₇, R₈, respectively. Theselarge radii of curvature R₇, R_(x) advantageously present a large,convex surface which minimizes pressure applied to adjacent soft tissuessuch as the retinaculum and extensor mechanism. In an exemplaryembodiment, radius R₇ is equal to radius R₈, with each of radii R₇, R₈sized as small as 5.0 mm, 5.3 mm or 5.5 mm and as large as 6.5 mm, 6.8mm or 7.0 mm, or are any size within any range defined by any of theforegoing values.

In some instances, the radii defined by the cross-sectional profile ofpatellar groove 60 are larger than radii R₇, R₈, such that the smallestradii presented across the entire medial/lateral extent ML_(G) of thearticular surface of anterior flange 22 are radii R₇, R₈. In theseinstances, no small radii are potentially presented to any adjacent softtissues.

Moreover, these radii represent a large proportion of the overallmedial/lateral width ML_(A) (FIG. 8) of anterior flange 22 at any givenmedial/lateral cross-section. For example, at the cross-section of FIG.8, medial/lateral flange width ML_(C) ranges from 37 to 53 mm across afamily of prosthesis sizes, such that radii R₇, R_(x) each definebetween 10% and 16% of overall medial/lateral width ML_(G) of anteriorflange 22.

By contrast, the corresponding radii defined by the prior art femoralcomponents of the Zimmer NexGen CR Flex prosthesis system define medialand lateral flange radii (analogous to radii R₇, R_(x) of the presentprosthesis) of between 2.0 mm and 2.6 mm across a range of seven nominalprosthesis sizes. Each of these prior art radii define between 3.5% and5.9% of the overall medial/lateral width (analogous to width ML_(G) ofthe present prosthesis) of the respective anterior flanges of the priorart femoral components.

7. Bone Conservation: Uniform Thickness of Anterior Flange.

FIG. 9A illustrates femoral component 20 having thickness ridge 300,which is disposed on the bone-contacting side of anterior flange 22 andspans across portions of anterior bone contacting surface 50 andanterior chamfer surface 52. As described in detail below, thicknessridge 300 defines a sagittally-oriented peak 302, which advantageouslyallows minimum thicknesses T_(T) (FIG. 8), T_(S)(FIG. 10A) in anteriorflange 22 to be maintained while preserving a surgeon's ability toimplant femoral component 20 on a distal femur with planar anterior andanterior chamfer facet cuts.

Turning to FIG. 9B, thickness ridge 300 includes ramped lateral facet304 and ramped medial facet 306, which gradually ascend toward oneanother to meet at peak 302. By contrast, a non-peaked thickness ridgemay include a single flat surface (illustrated schematically as surface300′ in FIG. 8), which extends medially/laterally without any peakedstructure. Viewed from a sagittal perspective, such as shown in FIG.10A, such non-peaked thickness ridge would follow the inner sagittalprofile of anterior bone contacting surface 50 and anterior chamfersurface 52 (shown in dashed lines). In contrast, as best seen in FIGS.10A and 10B, peak 302 of thickness ridge 300 protrudes inwardly frombone contacting surface 50 and anterior chamfer surface 52. In anexemplary embodiment, the amount of such inward protrusion may be up to1.5 mm to allow for implantation of femoral component 20 upon a bonewith planar resected surfaces, as discussed below.

Bone-contacting surfaces 50, 52, 54, 56, 58 (FIG. 9A) each extend from alateral edge to a medial edge of femoral component 20. Posterior surface58 and posterior chamfer surface 56 are each interrupted byintercondylar notch 68, such that surfaces 56, 58 each extend from themedial edge of condyle 26 to medial condylar wall 39, and from thelateral edge of lateral condyle 24 to lateral condylar wall 38.Together, bone-contacting surfaces 50, 52, 54, 56, 58 define the innersagittal profile of femoral component 20, which is the profile as itappears when the medial and lateral edges are superimposed over oneanother (i.e., aligned as illustrated in FIG. 1B).

Referring still to FIG. 9A, femoral component 20 includes lateral andmedial rails 59L, 59M which bound recessed pocket 31 adapted to receivebone cement, porous material, or other fixation material (e.g., fixationmaterial 33 as shown in FIG. 10B) for adhering femoral component 20 tothe distal femur upon implantation. Where rails 59L, 59M are provided,rails 59L, 59M are considered to define the inner sagittal periphery offemoral component 20 rather than the recessed profile of pocket 31.

Advantageously, peaked thickness ridge 300 allows for transversethickness T_(T) (FIG. 8) and sagittal thickness T_(S)(FIG. 10A) to bemaintained above a desired minimum thickness by providing extra materialfollowing the path of patellar groove 60 (FIG. 8). Thicknesses T_(T),T_(S) are measured as the shortest distance between the trough ofpatellar groove 60 (described above) and peak 302, and are equal whenmeasured between common points. The extra material provided by peak 302,corresponds with the profile of the deepest portion of the troughdefined by groove 60. In the exemplary embodiment illustrated in thedrawings, this deepest portion of groove 60 is also the portion thatdefines a series of points closest to the adjacent anterior andanterior-chamfer bone-contacting surfaces 50, 52 (e.g., FIGS. 7 and 8).Thus, what would normally be the thinnest portion of anterior flange 22is made thicker by peak 302. The overall minimum thickness of anteriorflange 22 may be as little as 1 mm, 1.1 mm or 1.3 mm and may be as largeas 1.8 mm, 1.9 mm or 2 mm, or may be any thickness within any rangedefined by any of the foregoing values. Generally speaking, largerprosthesis sizes have larger minimum thicknesses. Thicknesses T_(T),T_(S), are at least as large as, or greater than, the minimum.

Moreover, as illustrated in FIGS. 8 and 10A, the overall thickness ofanterior flange 22 is also more consistent across the medial/lateral andproximal/distal extent of anterior flange 22, as compared with athickness ridge having surface 300′ with a flat medial/lateral profile.This consistent thickness allows for the overall average thickness ofanterior flange 22 to be reduced to a value closer to the desiredminimum thickness, rather than providing the minimum thickness only nearpatellar groove 60 and excess thickness in the remainder of flange 22.This reduction in average flange thickness allows for reduced boneresection in the anterior facet and anterior chamfer, therebyfacilitating preservation of healthy bone stock. Further maintaininguniformity of thickness across medial/lateral extent ML_(G) facilitatesmanufacture of femoral component 20 by allowing for more even,consistent dissipation of heat, such as after forming, forging andmachining operations.

The uniformity of thickness across the medial/lateral cross-section ofanterior flange 22 may be expressed as the maximum deviation of anygiven thickness dimension as a percentage of the average thickness. Inan exemplary embodiment, this deviation may be as little as 38%, 39% or44% and as large as 55%, 58% or 65% of the average thickness, or may beany percentage of the average thickness within any range defined by anyof the foregoing values. The nominal range of average thicknesses acrossthe range of prosthesis sizes is between 2.2 mm and 3.7 mm. Theabove-mentioned thicknesses take into account the presence of recessedpocket 31, which defines recess depth D_(R) of between 1.1 and 1.2 mm.

By contrast, the prior art Zimmer NexGen CR Flex prosthesis systemincludes femoral components exhibit a corresponding maximum thicknessdeviation of between 35% and 46%, with the nominal range of averagethicknesses across a range of prosthesis sizes being between 3.4 mm and4.4 mm.

Peak 302 defines a relatively sharp edge along its longitudinal extent(FIG. 9B). In an exemplary embodiment, this sharp edge is manufacturedas an edged surface, such that the edge defines no appreciable radius asviewed in the medial/lateral cross section of FIG. 8. Because peak 302protrudes inwardly from bone contacting surface 50 and anterior chamfersurface 52 (as viewed from the sagittal perspective of FIG. 10A), thissharp edge operates to compact adjacent bone of the anterior facet andanterior chamfer facet when femoral component 20 is implanted on adistal femur. Such compaction is shown in FIG. 10B, where peak 302 isshown extending into the anterior and anterior chamfer facets ofresected femur F. More particularly, referring to FIG. 10C, femur F maybe prepared with planar anterior facet AF and planar anterior chamferfacet ACF. Once femoral component 20 is implanted upon femur F as shownin FIG. 10B, indentation I mimicking thickness ridge is formed by localcompaction of bone on facet AF and planar anterior chamfer facet ACF,thereby disrupting the planarity of facets AF, ACF in the region ofindentation I.

As compared with flat a prior art surface (shown schematically assurface 300′, shown in FIG. 8 and described above), the additionalvolume of bone displaced by the edge defined by peak 302 and theassociated elevation of lateral and medial facets 304, 306 is minimal.In an exemplary embodiment, the displaced volume may be as little as 0.8mm³, 1.2 mm³ or 1.5 mm³ and as large as 13.5 mm³, 13.7 mm³ or 13.8 mm³,or may be any volume within any range defined by any of the foregoingvalues. Moreover, the maximum inward protrusion of the edged peak 302 is1.5 mm past the sagittal geometry of anterior bone-contacting surface 50and anterior chamfer surface 52, as noted above.

Thus, the cancellous or cortical bone of the planar resected anteriorand anterior chamfer facets is easily compacted upon implantation offemoral component 20 to accommodate such additional volume. A surgeonmay make facet cuts in the femur which are substantially planar (asshown in FIG. 10C), thereby simplifying the surgical procedure. Thesefacet cuts may, for example, include five cuts to create five facetssized to receive anterior, anterior chamfer, distal, posterior chamferand posterior bone-contacting surfaces 50, 52, 54, 56, 58. Femoralcomponent 20 is provided by the surgeon, who then implants femoralcomponent 20 on the resected femur along a distal-to-proximal direction,until peaked portion 302 of thickness ridge 300 compresses the adjacentbone fully (as shown in FIG. 10B). When such full compression hasoccurred, indentation I is formed (FIG. 10D) such that the entireperiphery of thickness ridge 300 will be in contact with the adjacentfacets of the bone.

Optionally, to further ease bone compaction to accommodate peak 302,additional resection of the bone at the intersection of the anteriorfacet and anterior chamfer facet may be performed. For example, a smallosteotomy in the vicinity of peak 302 may be made prior to implantation,such as with a small saw blade, so that peak 302 sits within theosteotomy upon implantation. Similarly, a small hole may be made in thisarea, such as with a drill. However, testing performed by Applicants hasrevealed that no such osteotomy is necessary, and peak 302, lateralfacet 304 and medial facet 306 all seat firmly and completely oncortical and cancellous bone upon implantation.

An additional advantage conferred by peak thickness ridge 300 isadditional medial/lateral fixation of femoral component 20 uponimplantation. Once peak 302 has impacted the abutting bone, such facetsare no longer planar but instead include a ridge-shaped depressionoccupied by peak 302. Thus, lateral and medial facets 304, 306 act asbarriers to medial and lateral translation of femoral component 20, andthereby confer additional medial/lateral stability. This additionalstability aids in secure component fixation, particularly initiallyafter implantation.

It is contemplated that the overall size and geometry of thickness ridge300 may be constant across multiple femoral sizes, or may grow andshrink as femoral sizes grow larger or smaller. In an exemplaryembodiment, twelve femoral sizes are provided (as described in detailbelow), with the ten largest sizes including thickness ridge 300 havinga common size, shape and volume across all ten sizes. For the smallestsizes, a reduced-size thickness ridge 300A (FIG. 12A) may be used.

Overall medial/lateral extent ML_(R) (FIGS. 8 and 9B) andproximal/distal height H_(R)(FIGS. 9B and 10A) are calculated to be assmall as possible while maintaining a minimum desired thickness acrossthe entirety of anterior flange 22 (as discussed above). In an exemplaryembodiment, proximal/distal height H_(R) may be as little as 7.4 mm andas large as 14.5 mm, 14.6 or 15.0 mm, or may be any height within anyrange defined by any of the foregoing values. Medial/lateral extentML_(R) may be as little as 12.5 mm and as large as 15.0 mm, 15.1 or 15.5mm, or may be any volume within any range defined by any of theforegoing values. Within these dimensional bounds, the overallperipheral shape of thickness ridge 300 is designed to follow thecontours of anterior flange 22, advantageously providing visual acuitytherebetween.

For example, the changes in geometry for narrow anterior flange 122 ofnarrow femoral component 120 result in corresponding changes to theoverall shape of the corresponding thickness ridge (not shown), therebyproviding visual acuity with the narrow shape of component 120. However,the overall coverage area and design principles of thickness ridge 300apply to any femoral component made in accordance with the presentdisclosure.

Advantageously, maintaining medial lateral width ML_(R) andproximal/distal height H_(R) at minimum values serves to maximize thearea on anterior bone contacting surface 50 and anterior chamfer surface52 for fixation material, as described in detail below.

8. Bone Conservation: Intercondylar Notch with Sloped Sidewalls.

FIGS. 11A and 11B illustrate a sagittal cross-sectional view ofposterior stabilized femoral component 220, both before and afterimplantation upon resected femur F. The cross section of FIGS. 11A and11B are taken along the outer (i.e., lateral-facing) surface of lateralwall 238 of intercondylar notch 268. A similar cross-sectional view,taken at the medially-facing side of medial wall 239 of intercondylarnotch 268, would be a mirror image of FIGS. 11A and 11B. As illustrated,lateral wall 238 extends proximally from distal bone-contacting surface254 to define a height H_(IW) along the proximal/distal direction (e.g.,the direction perpendicular to distal bone contacting surface 254).

A posterior portion of wall 238 defines proximal edges (extending alongdistance D of FIGS. 11A and 11B) which are substantially parallel withdistal bone-contacting surface from the sagittal perspective of FIG.11A, while lateral wall 238 includes a downwardly sloping (i.e., in adistal direction) anterior portion 320. In an exemplary embodiment, theposterior and anterior portions define an overall anterior/posteriorextent of between 35 mm and 54 mm. The downward sloping anterior portion320 initiates at a distance D spaced anteroposteriorly from posteriorbone contacting surface 258, which is between 27 mm and 48 mm in theexemplary embodiment. Both distance D and the overall anterior/posteriorextent grow as sizes grow within a family of prosthesis sizes; acrosssuch a family of prosthesis sizes, distance D represents between 77% and89% of the overall anterior/posterior extent of wall 238.

Distance D is calculated to provide sufficient proximal/distal wallheight across the posterior portion of intercondylar notch 268, suchthat impingement of femur F upon spine 278 of tibial bearing component240 (FIG. 6) is avoided throughout the prosthesis range of motion.

Similarly, the angle 322 of sloped portion 320, taken with respect to atransverse plane (which, in the illustrated embodiment, is parallel todistal bone contacting surface 254), is also calculated to prevent spine278 from extending proximally beyond walls 238, 239 throughout the rangeof prosthesis motion. In extension, spine 278 sits between thenon-sloped portions of walls 238, 239 occupied by distance D (FIG. 11A).As flexion progresses, the proximal tip of spine 278 advances towardsloped portion 320 as femoral component 220 rotates with respect totibial bearing component 240. Angle 322 is calculated to provide spaceabove the proximal tip of spine 278 in deep flexion, while avoidingunnecessary resection of bone. Depending on the geometry of spine 278and the particular articular characteristics of the prosthesis, angle322 may be any acute angle greater than zero but less than 90 degrees.In an illustrative embodiment of FIGS. 11A and 11B angle 322 is 60degrees. The anterior location and gentle slope of anterior portion 320cooperate to position the anterior terminus of sloped portion 320 atanterior chamfer 252. As shown in FIGS. 11A and 11B, sloped portion 320terminates into anterior chamfer 252.

Advantageously, positioning the terminus of sloped portion 320 in arelatively anterior location, i.e., at anterior chamfer 252, preventsthe junction between walls 238, 239 and the adjacent bone-contactingsurfaces (252, 254, 256, 258) from interfering with any portion ofintercondylar notch 268. By contrast, for example, a very steep orvertical angle 322 for sloped portion 320 would cause sloped portion 320to terminate into an area occupied by intercondylar notch 268,potentially necessitating a change in the geometry and/or location ofintercondylar notch 268.

Advantageously, sloped portion 320 preserves bone stock of femur Fwithin area A in the anatomic intercondylar notch, thereby reducing theamount of bone which must be removed upon implantation of femoralcomponent 220. By contrast, anterior sagittal profile 320′, whichexcludes anterior sloped portion 320 and extends anteriorly along thesame profile as the top of lateral wall 238, would necessitate theremoval of the bone within area A. Although femur F is shown in FIGS.11A and 11B as having resection profiles that follow the sagittalprofile of intercondylar walls 238, 239, it is contemplate that incertain exemplary procedures the portion of the bone resectioncorresponding to sloped portion 320 may be extrapolated to the posteriorfacet (thereby yielding a substantially planar distal facet).

9. Bone Conservation: Intercondylar Fixation Lug.

For posterior stabilized femoral prosthesis designs, e.g., thoseincluding a femoral cam which articulates with a tibial bearingcomponent spine during articulation, fixation pegs 28 (FIG. 1B) may beomitted in favor of utilizing lateral and medial walls 238, 239 ofintercondylar notch 268 for fixation of femoral component 220 to thefemur.

For example, FIG. 12A shows femoral component 220 in a relativelysmaller component size which omits fixation pegs, instead offeringuninterrupted distal bone contacting surfaces 254. In order to fixcomponent 220 to femur F (FIGS. 11A and 11B), a function normallyprovided in part by pegs 28, walls 238, 239 of intercondylar notch 268may double as a fixation device. For example, a close tolerance betweenthe central lug defined by walls 238, 239 and the adjacent resected bonewithin the anatomic intercondylar notch may result in a friction-fittherebetween, thereby providing axial fixation of component 220 to femurF. In an exemplary embodiment, femoral component 220 including such acentral lug is implanted onto a femur with a nominal clearance of 0.76mm, and a range of clearances between 0.43 mm and 1.49 mm. Theseclearances may be provided through use of an appropriately sized cutguide designed for resection of the anatomic intercondylar fossa.

Advantageously, these exemplary clearances allow walls 238, 239 to beused as an axial fixation structure as described above, whilemaintaining acceptable stresses on the surrounding bone uponimplantation of femoral component 220. Further, because the naturalintercondylar notch naturally defines an anatomic void, use of walls238, 239 for fixation allows for only minimal resection of bone aroundthe periphery of the existing void, rather than creation of an entirelynew void within the bone stock of the distal femur.

Referring now to FIG. 12B, for example, lateral wall 238 may includerecessed cement pocket 330 formed therein. Medial wall 239 may include asimilar, laterally facing recessed cement pocket (not shown). Whenfemoral component 220 is implanted upon femur F, bone cement or porousfixation material may be disposed in the lateral and medial cementpockets 330 for fixation to the adjacent, resected bone within theintercondylar notch of the femur to augment the fixation of femoralcomponent 220 at bone contacting surfaces 250, 254, 258 and chamfers252, 256.

For example, pockets 330, bone contacting surfaces 250, 254, 258 and/orchamfers 252, 256 may be at least partially coated with a highly porousbiomaterial to facilitate firm fixation thereof to the abutting resectedsurfaces of the distal femur. A highly porous biomaterial is useful as abone substitute and as cell and tissue receptive material. A highlyporous biomaterial may have a porosity as low as 55%, 65%, or 75% or ashigh as 80%, 85%, or 90%, or may have any porosity within any rangedefined by any of the foregoing values. An example of such a material isproduced using Trabecular Metal™ Technology generally available fromZimmer, Inc., of Warsaw, Ind. Trabecular Metal™ is a trademark ofZimmer, Inc. Such a material may be formed from a reticulated vitreouscarbon foam substrate which is infiltrated and coated with abiocompatible metal, such as tantalum, by a chemical vapor deposition(“CVD”) process in the manner disclosed in detail in U.S. Pat. No.5,282,861 to Kaplan, the entire disclosure of which is hereby expresslyincorporated herein by reference. In addition to tantalum, other metalssuch as niobium, or alloys of tantalum and niobium with one another orwith other metals may also be used.

Generally, the porous tantalum structure includes a large plurality ofstruts (sometimes referred to as ligaments) defining open spacestherebetween, with each strut generally including a carbon core coveredby a thin film of metal such as tantalum, for example. The open spacesbetween the struts form a matrix of continuous channels having no deadends, such that growth of cancellous bone through the porous tantalumstructure is uninhibited. The porous tantalum may include up to 75%,85%, or more void space therein. Thus, porous tantalum is a lightweight,strong porous structure which is substantially uniform and consistent incomposition, and closely resembles the structure of natural cancellousbone, thereby providing a matrix into which cancellous bone may grow toprovide fixation of implant 10 to the patient's bone.

The porous tantalum structure may be made in a variety of densities inorder to selectively tailor the structure for particular applications.In particular, as discussed in the above-incorporated U.S. Pat. No.5,282,861, the porous tantalum may be fabricated to virtually anydesired porosity and pore size, and can thus be matched with thesurrounding natural bone in order to provide an improved matrix for boneingrowth and mineralization.

Alternatively, as shown in FIG. 12C, the laterally facing surface oflateral wall 238 may include surface texture 332 to aid in initial andlong term fixation of femoral component 220 to bone. Surface texture 332may include knurling, striations or scales, or any other suitabletexture. Similar to cement pocket 330, surface texture 332 may also beprovided on the medially facing surface of medial wall 239, such thatsurface texture 332 abuts resected bone in the intercondylar notch offemur F when femoral component 220 is implanted.

Omitting fixation pegs 28 and utilizing walls 238, 239 of intercondylarnotch 268 is particularly advantageous in the context of small componentsized for use with small stature patients. In these instances, a limitedamount of distal bone area is available for fixation of femoralcomponent 220, which may leave insufficient fixation space betweenfixation pegs 28 and walls 238, 239 of intercondylar notch 268. Byomitting femoral fixation pegs 28 and instead using walls 238, 239 forfixation as described above, additional natural bone may be preserved toprovide enhanced structural integrity and robustness of the distalfemur.

For small stature patients, the medial/lateral width or gap betweenlateral and medial walls 238, 239 of intercondylar notch 268 may bereduced. This may allow for walls 238, 239 to have increased contactwith cortical bone in a relatively narrower anatomic intercondylar notchtypical of small stature distal femurs.

Referring now to FIG. 12D, an optional auxiliary fixation lug 334 may beprovided to further enhance fixation of femoral component 220 to thefemur. Auxiliary lug 334 extends laterally from the lateral face oflateral wall 238, and spans the angular corner formed by lateral wall238 and the adjacent portion of distal bone contacting surface 254,thereby forming a fin-like structure protruding outwardly from wall 238.A similar auxiliary fin (not shown) may also extend medially from themedial face of medial wall 239.

Auxiliary lug 334 increases the bone-contacting surface area provided byfemoral component 220, thereby enhancing the strength of fixation ofcomponent 220 to the distal resected femur. The surfaces of auxiliarylug 334 may be affixed to the bone by porous material, bone cement orsurface texture, for example, in a similar fashion to the lateral andmedial faces of walls 238, 239 as discussed above.

In use, a slot is resected in the distal resected surface of the femur,with the slot sized and positioned to accommodate auxiliary lug 334.Advantageously, the resected slots in the femur are clearly visible tothe surgeon as femoral component 220 is advanced toward the femur uponfinal implantation. If the anterior and distal facets of the femur(i.e., the resected surfaces created to abut anterior and posteriorbone-contacting surfaces 250, 258 respectively) are obscured duringimplantation, such as by the adjacent tissues of the knee, the surgeonwill nevertheless be able to visualize the proper implanted orientationof femoral component 220 by aligning auxiliary lug 324 to the visibleresected slot in the distal femur, and then verify such alignment bytactile feedback as femoral component 220 is seated upon the resectedbone surface.

In the illustrated embodiment, auxiliary lug 334 has a generallytriangular shape and is substantially perpendicular to lateral wall 238.However, it is contemplated that auxiliary lug 334 may have other shapesand/or spatial arrangements. For example, lug 334 may have roundedcorners, squared corners, and/or leading edges that are pointed, roundedor squared.

10. Bone Conservation: Reduced Incremental Growth Between Sizes.

Referring now to FIG. 13A, anteroposterior sizing extent 340 of femoralcomponent 20 is illustrated. Extent 340 is measured beginning fromintersection point 342 between anterior bone contacting surface 50 anddistal bone contacting surface 54, with surfaces 50, 54, extrapolateddistally and anteriorly to form intersection point 342. The other end ofextent 340 is posterior-most contact points 34 and/or 36 (discussed indetail above).

As noted herein, an exemplary knee prosthesis system in accordance withthe present disclosure includes twelve separate component sizes, each ofwhich defines a different and unique anteroposterior sizing extent 340.As between any adjacent pair of sizes (e.g. sizes 1 and 2, sizes 6 and 7or sizes 11 and 12), a common difference 344 is defined between therespective anteroposterior extents 340 of the pair of sizes, as shown inFIG. 13B. FIG. 13B illustrates that difference 344 is 2 mm across arange of prosthesis sizes, while corresponding prior art size rangeshave corresponding differences that are larger than 2 mm and notconsistent across the range of sizes. In an exemplary embodiment, theassociated family of femoral prostheses may be as little as 3 sizes andas large as 12 sizes. The prior art devices shown in FIG. 13B includecruciate-retaining designs, in particular the femoral components of theprior art Zimmer NexGen CR Flex prosthesis system, discussed above, andfemoral components of the prior art Zimmer NexGen CR prosthesis system,shown in the “NexGen Complete Knee Solution, Implant Options,Surgeon-Specific,” submitted on even date herewith in an InformationDisclosure Statement, the entire disclosure of which is hereby expresslyincorporated herein by reference. FIG. 13B also includesposterior-stabilized prior art designs, in particular the femoralcomponents of the prior art Zimmer NexGen LPS Flex prosthesis system,and the femoral components of the prior art Zimmer NexGen LPS prosthesissystem, shown in the “Zimmer® NexGen® LPS-Flex Mobile and LPS-MobileBearing Knees” product brochure and “Zimmer® NexGen® LPS Fixed Knee,Surgical Technique”, both submitted on even date herewith in anInformation Disclosure Statement, the entire disclosures of which arehereby expressly incorporated herein by reference.

Advantageously, measuring anteroposterior extent 340 from the virtualintersection point 342 to posterior most contact point 34 establishessize increments irrespective of changes to anterior flange 22 acrosssizes. For example, as shown in FIG. 13A, anterior flange 50A of thenext incrementally larger-size femoral component 20A is longer andwider. Therefore, difference 344, designed to be constant amongrespective adjacent pairs of sizes, would be effected by this changinggeometry of flange 22A.

However, it is desirable to include only incremental anteroposteriorgrowth/shrinkage of posterior most contact point 34A in selecting sizeincrements, so that a change in size has a predictable effect onmid-flexion soft tissue balancing of the knee. Thus, incremental sizegrowth having a common anteroposterior difference 344 defined betweenany respective pair of sizes provides a uniform and consistent effect onsoft tissue balancing as between any pair of sizes across the sizerange. This, in turn, promotes shorter operative times and allows forimplant designers to optimize anterior flange 22 without impacting theconsistency of growth between sizes. Further, by providing twelvestandard sizes with unique anteroposterior extents 340, greater patientspecificity may be achieved as compared with alternative systems havingfewer size options.

In an exemplary embodiment, a surgeon may resect a patient's femur toaccept the largest of a range of candidate prosthesis sizes identifiedby the surgeon (such as, for example, by pre-operative imaging). If thesurgeon subsequently decides to “downsize” to the next-smallest size offemoral component 20, the posterior and posterior-chamfer facets of theresected bone surface (i.e., the facets corresponding to posteriorchamfer surface 56 and posterior surface 58) may be further resected,with 2 mm of bone removed from posterior surface 58 to correspond toanteroposterior difference 344. To effect such further resection, anappropriately configured cutting guide may be used. Alternatively, thesurgeon may employ a provisional femoral component utilizingappropriately sized resection slots, such as by using the system andmethod disclosed in U.S. Patent Application Publication Serial No.2012/0078263, filed Sep. 9, 2011 and entitled BONE PRESERVINGINTRAOPERATIVE DOWNSIZING SYSTEM FOR ORTHOPAEDIC IMPLANTS (AttorneyDocket No. ZIM0816-01), the entire disclosure of which is herebyexpressly incorporated herein by reference.

11. Bone Conservation: Revisable Bone Contacting Fixation Area.

As shown in FIG. 14A, femoral component 20 includes recessed pocket 336formed as part of bone contacting surfaces 50, 54 and 58 and chamfers52, 56. Recessed pocket 336 is surrounded by peripheral rail 337,similar to medial and lateral rails 59M, 59L shown in FIG. 9A anddiscussed in detail above. Recessed pocket 336 is interrupted byfixation pegs 28 and thickness ridge 300. Aside from the small areasoccupied by rail 337, pegs 28 and ridge 300, the entirety of bonecontacting surfaces 50, 54 and 58 and chamfers 52 and 56 are availableto receive cement or porous ingrowth material for fixation of femoralcomponent 20 to the adjacent resected facets on the distal femur. In anexemplary embodiment, rails 59M, 59L are elevated above the surfaces ofrecessed pocket 336 by between 1.1 and 1.2 mm.

Advantageously, recessed pocket 336 is larger than alternative devicesby up to 40%, thereby providing a larger fixation area for more robustfixation to the distal femur. More particularly, in an exemplaryembodiment femoral component 20 may have a total fixation area withinrecessed pocket 336 of as little as 2272 mm³ for a small-size prosthesisand as much as 5343 mm³ for a large-size prosthesis, representingbetween 79% and 88% of the total aggregated surface area ofbone-contacting surfaces 50, 52, 54, 56, 58 across all prosthesis sizes.Advantageously, this range of surface area coverage represents anincrease in surface area coverage of at least 14%, as compared tocomparable prosthesis sizes in the above-mentioned prior artcruciate-retaining prostheses.

In some instances, it may be necessary to perform a revision surgery inwhich femoral component 20 is removed from the distal femur and replacedwith a new femoral component. In order to facilitate this process,osteotome 350 having blade 352 may access the entirety of recessedpocket 336 either from the outer periphery along rail 337, or viaintercondylar notch 68 and the intercondylar portion of rail 337. Whenblade 352 is worked around the entirety of rail 337 in this way, all ofthe bone cement or porous fixation material may be dislodged from thedistal femur by osteotome 350. Full dislodging femoral component 20 fromthe distal femur prior to removal in a revision surgery protects theintegrity of the remaining bone.

Turning now to FIG. 14B, posterior stabilized femoral component 220includes recessed pocket 338 surrounded by rail 237, which are generallysimilar to recessed pocket 336 and rail 337 described above. In anexemplary embodiment, rail 237 is elevated above the surfaces ofrecessed pocket 338 by between 1.1 and 1.2 mm. However, the proximallyextending lateral and medial intercondylar walls 238, 239 ofintercondylar notch 268 (described in detail above) preclude blade 352of osteotome 350 from accessing the bone-contacting space between walls238, 239 and adjacent fixation pegs 28.

To facilitate potential revision surgery, femoral component 220 includesrecessed pocket interruptions in the form of lateral and medial ridges346, 348. Lateral ridge 346 directly abuts the distal resected facet onfemur F (FIG. 11) when femoral component 220 is implanted thereon,thereby preventing bone cement or porous ingrowth material frominhabiting the space between lateral wall 238 and peg 28. Similarly,medial ridge 348 occupies the space between medial wall 239 and peg 28,also preventing bone cement or porous ingrowth material from inhabitingthis space upon implantation. In an exemplary embodiment, ridges 346,348 are elevated above the surrounding surfaces of recessed pocket 338by the same amount as rail 337, i.e., between 1.1 and 1.2 mm.

Referring still to FIG. 14B, lateral and medial ridges 346, 348 defineridge sidewalls disposed entirely anterior or posterior of the peripheryof pegs 28, (i.e., as viewed “from the side” in a sagittal plane or“from the top” in a transverse plane). Thus, no portion of the sidewallsof ridges 346, 348 is inaccessible to blade 352 of osteotome 350 asblade 352 enters from rail 237 and sweeps along a medial-to-lateral orlateral-to-medial direction. Accordingly, blade 352 can reach everyother portion of recessed pocket 338 via rail 237 surrounding outerperiphery of femoral component 220 in similar fashion as describedabove. Accordingly, femoral component 220 may be fully dislodged fromfemur F prior to removal therefrom during revision surgery.

Similar to recessed pocket 336 discussed above, recessed pocket 338 isalso larger than alternative devices by up to 40%, thereby providing alarger fixation area for more robust fixation to the distal femur. Moreparticularly, in an exemplary embodiment femoral component 220 may havea total fixation area within recessed pocket 338 of as little as 2128mm³ for a small-size prosthesis and as much as 4780 mm³ for a large-sizeprosthesis, representing between 77% and 85% of the total aggregatedsurface area of bone-contacting surfaces 50, 52, 54, 56, 58 across allprosthesis sizes. Advantageously, this range of surface area coveragerepresents an increase in surface area coverage of at least 15%, ascompared to comparable prosthesis sizes in the above-mentioned prior artposterior-stabilized prostheses.

While the disclosure has been described as having exemplary designs, thepresent disclosure can be further modified within the spirit and scopeof this invention. This application is therefore intended to cover anyvariations, uses or adaptations of the disclosure using its generalprinciples. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this disclosure pertains.

1-23. (canceled)
 24. A femoral component adapted to articulate with a tibial articular surface and a patellar articular surface in a knee prosthesis, said femoral component comprising: a medial condyle comprising: a medial condylar surface shaped to articulate with a medial compartment of the tibial articular surface through a range of motion; and a medial posterior bone-contacting surface disposed opposite said medial condylar surface and positioned to abut a posterior facet of a resected femur upon implantation of the femoral component, said medial posterior bone-contacting surface extending between a medial edge of said femoral component and a medial intercondylar wall; a lateral condyle separated from said medial condyle by a component sagittal plane, said lateral condyle comprising: a lateral condylar surface shaped to articulate with a lateral compartment of the tibial articular surface through the range of motion; and a lateral posterior bone-contacting surface disposed opposite said lateral condylar surface and positioned to abut the posterior facet of the resected femur upon implantation of the femoral component, said lateral posterior bone-contacting surface extending between a lateral edge of said femoral component and a lateral intercondylar wall facing said medial intercondylar wall; and a patellar flange extending anteriorly from said medial and lateral condyles, said patellar flange comprising: a flange articular surface shaped to articulate with the patellar articular surface; an anterior bone-contacting surface disposed opposite said flange articular surface and positioned to abut an anterior facet of the resected femur upon implantation of the femoral component, said anterior bone-contacting surface extending between said lateral edge of said femoral component and said medial edge of said femoral component; and a distal bone-contacting surface extending along an anterior/posterior space between said anterior bone-contacting surface and said medial and lateral posterior bone-contacting surfaces, said distal bone-contacting surface extending between said lateral edge of said femoral component and said medial edge of said femoral component, said medial and lateral edges of said femoral component defining an inner sagittal profile, as viewed in the component sagittal plane such that said medial edge of said femoral component is superimposed over said lateral edge of said femoral component, and said medial and lateral edges comprising medial and lateral rails protruding inwardly to define a recessed pocket between said medial and lateral rails, said femoral component comprising at least one lateral fixation peg and at least one medial fixation peg, said lateral fixation peg extending proximally from said distal bone-contacting surface and spaced laterally away from said lateral intercondylar wall such that a lateral portion of said distal bone-contacting surface is disposed between said lateral fixation peg and said lateral intercondylar wall, said medial fixation peg extending proximally from said distal bone-contacting surface and spaced medially away from said medial intercondylar wall such that a medial portion of said distal bone-contacting surface is disposed between said medial fixation peg and said medial intercondylar wall, at least one of said medial portion and said lateral portion of said distal bone-contacting surface occupied by a ridge rising above said recessed pocket, said ridge elevated above said recessed pocket by substantially the same amount as said medial and lateral rails such that said ridge is substantially coincident with said inner sagittal profile as viewed in the component sagittal plane, whereby said ridge interrupts any fixation material which may be contained within the recessed pocket upon implantation of the femoral component to a distal femur.
 25. The femoral component of claim 24, wherein: said ridge comprises an anterior sidewall disposed entirely anterior of a periphery of at least one of said medial fixation peg and said lateral fixation peg; and said ridge comprises a posterior sidewall disposed entirely posterior of the periphery of at least one of said medial fixation peg and said lateral fixation peg, whereby no portion of said anterior and posterior sidewalls of said ridge are inaccessible to an osteotome blade when said femoral component is fixed to the distal femur.
 26. The femoral component of claim 24, wherein said ridge is elevated above said recessed pocket by between 1.1 and 1.2 mm.
 27. The femoral component of claim 24, wherein said recessed pocket comprises a total pocket area equal to at least 77% of an aggregated surface area of said medial and lateral posterior bone-contacting surface, said anterior bone-contacting surface, and said distal bone-contacting surface.
 28. The femoral component of claim 27, wherein said total pocket area is equal to up to 85% of said aggregated surface area.
 29. The femoral component of claim 27, wherein said total pocket area of said recessed pocket is between 2128 mm³ and 4780 mm; depending on the nominal size of said femoral component.
 30. The femoral component of claim 24, wherein an intercondylar space is formed between said medial and lateral intercondylar walls, said femoral component comprising a femoral cam spanning said intercondylar space to join said medial and lateral condyles to one another, said femoral cam sized and positioned to engage a spine extending proximally from the tibial articular surface in positive flexion through at least a portion of the range of motion, whereby said femoral component comprises a posterior-stabilized femoral component. 